editor: Preserve active search match on panel open

[hlcfan]

Description

Preserve the active editor search occurrence when Find is closed and reopened with the same query.

An unchanged query now keeps the matcher’s current index and is not re-anchored to the viewport. New queries and case-sensitivity changes still rebuild and anchor the search normally. This also prevents the styled search panel’s initial query synchronization from resetting the occurrence.

Screenshot

Before

Before.mov

After

After.mov

How to test

1. Search for a term with at least three matches.
2. Navigate to the second match and close Find.
3. Reopen Find without changing the query.
4. Confirm the counter remains at 2/3 and Next advances to 3/3.

cargo test -p gpui-base input::search::tests
cargo test -p gpui-component input::overlay::tests

AI assistance: Codex generated the implementation and regression tests; I reviewed changes.

Checklist

• I have read the CONTRIBUTING document and followed the guidelines.
• Reviewed the changes in this PR and confirmed AI-generated code (if any) is accurate.
• Passed cargo run for story tests related to the changes.
• Platform-specific performance testing is not applicable; this is platform-independent search state synchronization.