#20091 Ignore symlinked directories in source ignores

Summary

Preserves symlink paths when optimizing negated @source not entries, so ignores are matched against the same path shape the scanner sees while following symlinks.

This fixes cases where @source not "./symlink" was optimized to the symlink target path and therefore failed to ignore files discovered through the symlink.

Fixes #17985

Test plan

• cargo fmt --check
• cargo test -p tailwindcss-oxide test_source_not_can_ignore_symlinked_directory --test scanner
• cargo test -p tailwindcss-oxide --test scanner