Fix relative imports when renaming files

[xaskii]

Summary

Fixes #4055

• We resolve relative imports against the importing module when updating imports for willRenameFiles.
• This fixes renames like pkg/a.py to pkg/a2.py, where from .a import foo should become from .a2 import foo.
• If a move takes the module outside the package targeted by the leading dots, we update the import to an absolute path instead.

Test Plan

• uv run --with jsonschema --with toml test.py
• Added regression tests for renaming within a package and moving outside it.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅