[syntax-errors] Store to or delete __debug__ (#16984)

Summary
--

Detect setting or deleting `__debug__`. Assigning to `__debug__` was a
`SyntaxError` on the earliest version I tested (3.8). Deleting
`__debug__` was made a `SyntaxError` in [BPO 45000], which said it was
resolved in Python 3.10. However, `del __debug__` was also a runtime
error (`NameError`) when I tested in Python 3.9.6, so I thought it was
worth including 3.9 in this check.

I don't think it was ever a *good* idea to try `del __debug__`, so I
think there's also an argument for not making this version-dependent at
all. That would only simplify the implementation very slightly, though.

[BPO 45000]: https://github.com/python/cpython/issues/89163

Test Plan
--

New inline tests. This also required adding a `PythonVersion` field to
the `TestContext` that could be taken from the inline `ParseOptions` and
making the version field on the options accessible.

crates/ruff_python_parser/src/parser/options.rs

@@ -34,6 +34,10 @@ impl ParseOptions {
         self.target_version = target_version;
         self
     }
+
+    pub fn target_version(&self) -> PythonVersion {
+        self.target_version
+    }
 }
 
 impl From<Mode> for ParseOptions {