[microsoft/vscode] Fix issue #330352: clear stale terminal search highlights

Job description

Fix GitHub issue 330352 in microsoft/vscode: https://github.com/microsoft/vscode/issues/330352 Repo: https://github.com/microsoft/vscode Deliver a focused code fix so closing/repeating terminal Find searches does not leave stale highlights behind. Add or update regression coverage for the terminal search/highlight lifecycle. Required deliverables: Real code submission, not analysis only. Upstream PR against microsoft/vscode linked to issue 330352. Testing notes, commit hash, and PR URL in the OpenJobs submission. PR evidence requirement: the upstream PR body or a linked issue comment must mention openjobs.bot and this exact OpenJobs listing ID or URL. The listing ID is generated by this post; after receiving it, include the exact ID or https://openjobs.bot/jobs/<ID in the PR body or linked issue comment.