Support iOS platform tags (#15640)

## Summary
This implements the iOS part of
https://github.com/astral-sh/uv/issues/8029

FYI: @freakboy3742

<!-- What's the purpose of the change? What does it do, and why? -->

## Test Plan
Create a venv with uv and run `cargo run pip install --python-platform
arm64-apple-ios pillow`. Then the iOS binary of pillow should be
installed inside the venv.

crates/uv-configuration/src/target_triple.rs

@@ -257,6 +257,30 @@ pub enum TargetTriple {
     /// A wasm32 target using the Pyodide 2024 platform. Meant for use with Python 3.12.
     #[cfg_attr(feature = "clap", value(name = "wasm32-pyodide2024"))]
     Wasm32Pyodide2024,
+
+    /// An ARM64 target for iOS device
+    ///
+    /// By default, iOS 13.0 is used, but respects the `IPHONEOS_DEPLOYMENT_TARGET`
+    /// environment variable if set.
+    #[cfg_attr(feature = "clap", value(name = "arm64-apple-ios"))]
+    #[serde(rename = "arm64-apple-ios")]
+    Arm64Ios,
+
+    /// An ARM64 target for iOS simulator
+    ///
+    /// By default, iOS 13.0 is used, but respects the `IPHONEOS_DEPLOYMENT_TARGET`
+    /// environment variable if set.
+    #[cfg_attr(feature = "clap", value(name = "arm64-apple-ios-simulator"))]
+    #[serde(rename = "arm64-apple-ios-simulator")]
+    Arm64IosSimulator,
+
+    /// An `x86_64` target for iOS simulator
+    ///
+    /// By default, iOS 13.0 is used, but respects the `IPHONEOS_DEPLOYMENT_TARGET`
+    /// environment variable if set.
+    #[cfg_attr(feature = "clap", value(name = "x86_64-apple-ios-simulator"))]
+    #[serde(rename = "x86_64-apple-ios-simulator")]
+    X8664IosSimulator,
 }
 
 impl TargetTriple {
@@ -510,6 +534,48 @@ impl TargetTriple {
                 });
                 Platform::new(Os::Android { api_level }, Arch::X86_64)
             }
+            Self::Arm64Ios => {
+                let (major, minor) = ios_deployment_target().map_or((13, 0), |(major, minor)| {
+                    debug!("Found iOS deployment target: {}.{}", major, minor);
+                    (major, minor)
+                });
+                Platform::new(
+                    Os::Ios {
+                        major,
+                        minor,
+                        simulator: false,
+                    },
+                    Arch::Aarch64,
+                )
+            }
+            Self::Arm64IosSimulator => {
+                let (major, minor) = ios_deployment_target().map_or((13, 0), |(major, minor)| {
+                    debug!("Found iOS deployment target: {}.{}", major, minor);
+                    (major, minor)
+                });
+                Platform::new(
+                    Os::Ios {
+                        major,
+                        minor,
+                        simulator: true,
+                    },
+                    Arch::Aarch64,
+                )
+            }
+            Self::X8664IosSimulator => {
+                let (major, minor) = ios_deployment_target().map_or((13, 0), |(major, minor)| {
+                    debug!("Found iOS deployment target: {}.{}", major, minor);
+                    (major, minor)
+                });
+                Platform::new(
+                    Os::Ios {
+                        major,
+                        minor,
+                        simulator: true,
+                    },
+                    Arch::X86_64,
+                )
+            }
         }
     }
 
@@ -555,6 +621,9 @@ impl TargetTriple {
             Self::Aarch64LinuxAndroid => "aarch64",
             Self::X8664LinuxAndroid => "x86_64",
             Self::Wasm32Pyodide2024 => "wasm32",
+            Self::Arm64Ios => "arm64",
+            Self::Arm64IosSimulator => "arm64",
+            Self::X8664IosSimulator => "x86_64",
         }
     }
 
@@ -600,6 +669,9 @@ impl TargetTriple {
             Self::Aarch64LinuxAndroid => "Android",
             Self::X8664LinuxAndroid => "Android",
             Self::Wasm32Pyodide2024 => "Emscripten",
+            Self::Arm64Ios => "iOS",
+            Self::Arm64IosSimulator => "iOS",
+            Self::X8664IosSimulator => "iOS",
         }
     }
 
@@ -648,6 +720,9 @@ impl TargetTriple {
             // https://github.com/emscripten-core/emscripten/blob/4.0.8/system/lib/libc/emscripten_syscall_stubs.c#L63
             // It doesn't really seem to mean anything? But for completeness we include it here.
             Self::Wasm32Pyodide2024 => "#1",
+            Self::Arm64Ios => "",
+            Self::Arm64IosSimulator => "",
+            Self::X8664IosSimulator => "",
         }
     }
 
@@ -695,6 +770,9 @@ impl TargetTriple {
             // This is the Emscripten compiler version for Pyodide 2024.
             // See https://pyodide.org/en/stable/development/abi.html#pyodide-2024-0
             Self::Wasm32Pyodide2024 => "3.1.58",
+            Self::Arm64Ios => "",
+            Self::Arm64IosSimulator => "",
+            Self::X8664IosSimulator => "",
         }
     }
 
@@ -740,6 +818,9 @@ impl TargetTriple {
             Self::Aarch64LinuxAndroid => "posix",
             Self::X8664LinuxAndroid => "posix",
             Self::Wasm32Pyodide2024 => "posix",
+            Self::Arm64Ios => "posix",
+            Self::Arm64IosSimulator => "posix",
+            Self::X8664IosSimulator => "posix",
         }
     }
 
@@ -785,6 +866,9 @@ impl TargetTriple {
             Self::Aarch64LinuxAndroid => "android",
             Self::X8664LinuxAndroid => "android",
             Self::Wasm32Pyodide2024 => "emscripten",
+            Self::Arm64Ios => "ios",
+            Self::Arm64IosSimulator => "ios",
+            Self::X8664IosSimulator => "ios",
         }
     }
 
@@ -830,6 +914,9 @@ impl TargetTriple {
             Self::Aarch64LinuxAndroid => false,
             Self::X8664LinuxAndroid => false,
             Self::Wasm32Pyodide2024 => false,
+            Self::Arm64Ios => false,
+            Self::Arm64IosSimulator => false,
+            Self::X8664IosSimulator => false,
         }
     }
 
@@ -863,6 +950,20 @@ fn macos_deployment_target() -> Option<(u16, u16)> {
     Some((major, minor))
 }
 
+/// Return the iOS deployment target as parsed from the environment.
+fn ios_deployment_target() -> Option<(u16, u16)> {
+    let version = std::env::var(EnvVars::IPHONEOS_DEPLOYMENT_TARGET).ok()?;
+    let mut parts = version.split('.');
+
+    // Parse the major version (e.g., `12` in `12.0`).
+    let major = parts.next()?.parse::<u16>().ok()?;
+
+    // Parse the minor version (e.g., `0` in `12.0`), with a default of `0`.
+    let minor = parts.next().unwrap_or("0").parse::<u16>().ok()?;
+
+    Some((major, minor))
+}
+
 /// Return the Android API level as parsed from the environment.
 fn android_api_level() -> Option<u16> {
     let api_level_str = std::env::var(EnvVars::ANDROID_API_LEVEL).ok()?;