Fix line offsets when incremental edits join CRLF

[ammann (agammann)]

Bug

An incremental edit can join a carriage return and line feed across the edit boundary while leaving the cached line offsets stale. For example, inserting \n at line 1, character 0 in a\rb produces a\r\nb, but lineCount returns 3 instead of 2. Line and position lookups then disagree with a fresh document containing the same text.

Fix

Invalidate cached line offsets when an edit leaves a CRLF pair across either edit boundary. The next lookup rebuilds them from the updated content; other edits retain the incremental update path.

Verification

• The new regression failed on unmodified b4f995b (3 !== 2) and passes with this fix. It covers insertion at either side of the boundary, removal of an intervening character, and a batch of edits.
• textDocument: npm run all (63 tests passing).
• Repository: npm run symlink, npm run compile, npm run lint, and npm test passed locally on Node 22.
• On this Ubuntu 26.04 host, Playwright's browser suites used its Ubuntu 24.04 Chromium build via PLAYWRIGHT_HOST_PLATFORM_OVERRIDE=ubuntu24.04-x64.