Rollup merge of #148159 - politikl:move-rustdoc-tests-to-subdirs, r=GuillaumeGomez

Move rustdoc tests to appropriate subdirectories

## Summary

This PR reorganizes rustdoc tests into their correct subdirectories for better categorization and maintainability.

## Changes

- Moved 6 lint-related tests to `tests/rustdoc-ui/lints/`
- Moved 2 intra-doc link tests to `tests/rustdoc-ui/intra-doc/`
- Moved 3 deref-related tests to `tests/rustdoc-ui/deref/`
- Moved 1 doc-cfg test to `tests/rustdoc/doc-cfg/`

## Tests

All moved tests have been verified and pass in their new locations.

Author: matthiaskrgr