[ty] Emit error for invalid binary operations in type expressions (#18991)

## Summary

This PR adds diagnostic for invalid binary operators in type
expressions. It should close https://github.com/astral-sh/ty/issues/706
if merged.

Please feel free to suggest better wordings for the diagnostic message.

## Test Plan

I modified `mdtest/annotations/invalid.md` and added a test for each
binary operator, and fixed tests that was broken by the new diagnostic.

crates/ty_python_semantic/resources/mdtest/annotations/string.md

@@ -154,6 +154,7 @@ shouldn't panic.
 ```py
 a: "1 or 2"
 b: "(x := 1)"
+# error: [invalid-type-form]
 c: "1 + 2"
 d: "lambda x: x"
 e: "x if True else y"