Add Pyodide support (#12731)

This includes some initial work on adding Pyodide support (issue
#12729). It is enough to get
```
uv pip compile -p /path/to/pyodide --extra-index-url file:/path/to/simple-index
```
to work which should already be quite useful.

## Test Plan

* added a unit test for `pyodide_platform`
* integration tested manually with:
```
cargo run pip install \
-p /home/rchatham/Documents/programming/tmp/pyodide-venv-test/.pyodide-xbuildenv-0.29.3/0.27.4/xbuildenv/pyodide-root/dist/python \
--extra-index-url file:/home/rchatham/Documents/programming/tmp/pyodide-venv-test/.pyodide-xbuildenv-0.29.3/0.27.4/xbuildenv/pyodide-root/package_index \
--index-strategy unsafe-best-match --target blah --no-build \
numpy pydantic
```

---------

Co-authored-by: konsti <konstin@mailbox.org>
Co-authored-by: Zanie Blue <contact@zanie.dev>

crates/uv-python/python/get_interpreter_info.py

@@ -510,6 +510,24 @@ def get_operating_system_and_architecture():
             "major": int(version[0]),
             "minor": int(version[1]),
         }
+    elif operating_system == "emscripten":
+        pyodide_abi_version = sysconfig.get_config_var("PYODIDE_ABI_VERSION")
+        if not pyodide_abi_version:
+            print(
+                json.dumps(
+                    {
+                        "result": "error",
+                        "kind": "emscripten_not_pyodide",
+                    }
+                )
+            )
+            sys.exit(0)
+        version = pyodide_abi_version.split("_")
+        operating_system = {
+            "name": "pyodide",
+            "major": int(version[0]),
+            "minor": int(version[1]),
+        }
     elif operating_system in [
         "freebsd",
         "netbsd",