Python: regenerate stale type stubs and fix typing imports in stub generator

[knutwannheden]

Motivation

The auto-generated .pyi type stubs in rewrite-python had drifted from their source modules. The most visible symptom: markers.pyi declared SearchResult but omitted all Markup* classes (Markup, MarkupWarn, MarkupError, MarkupInfo, MarkupDebug), which were added to markers.py two days after the stubs were last regenerated. Regenerating showed 8 stub files were stale (nothing checks stub freshness, which is how they drifted).

Regenerating also surfaced a pre-existing bug in scripts/generate_stubs.py: it hardcoded from typing import Any, ClassVar, List, Optional (plus optional TypeVar, Generic) and never imported other typing names actually used in annotations — Dict, Callable, Type, Iterable, IO, or Generic used as a base class — so the generated stubs referenced names that were never imported.

Summary

• Generator: import the typing names a stub actually uses. Added collect_typing_names, which scans annotation contexts (fields, parameters, return types) and class base expressions (for Generic[...]/Protocol[...]) for names in typing.__all__, and appends them to the header import — keeping Any, ClassVar, List, Optional first and TypeVar, Generic last to minimize diff churn.
• Generator: avoid false imports from local-name collisions. Added collect_defined_names so a name shadowed by a local class/function/import (e.g. J.Literal, Py.TypeAlias, JavaType.Union — all collide with typing.__all__) is not wrongly imported from typing. Names imported from typing in the source are preserved (they are exactly what the stub must re-import).
• Regenerated all stub files from current sources: markers.pyi, parser.pyi, tree.pyi, java/tree.pyi, java/support_types.pyi, python/markers.pyi, python/support_types.pyi, python/tree.pyi.

Test plan

• All regenerated stubs parse as valid Python (ast.parse).
• Every typing name referenced (in Load context) in each stub is resolvable — either imported or defined locally as a class — verified via an AST check across all stubs.
• Generator is idempotent: a second python scripts/generate_stubs.py run produces zero further changes.