Tracking issue for grammar mistakes involving the word "which"

Some of the "which" issues are quite clear:

- redundant preposition: "the world **in** **which** we live **in**"
- "in which" where just "which" alone should be used.

But some are more convoluted or fuzzy and fit both categories or neither of them or are hard to classify.

No file, test, or entry point is identified. Start by locating the existing handling and tests for grammar cases involving “which,” then classify the listed examples and agree on the intended behavior for ambiguous cases. Done means the categories are resolved and the corresponding checker behavior is covered by tests.

Written by the indexing model from the issue text.