fix(vscode): migrate deprecated vscode-test to @vscode/test-electron

The Windows test jobs failed with "Failed to get VS Code archive location".
The deprecated vscode-test@1.6.1 hardcodes the legacy `win32-archive`
(32-bit) platform, which modern VS Code (1.126.0) no longer publishes, so
the download URL could not be resolved on Windows (Linux/macOS were
unaffected as their platform strings still exist).

Migrate the integration-test harness to the maintained successor
@vscode/test-electron ^2.5.2, which resolves `win32-x64-archive`. Pinned to
the 2.x line because 3.x requires Node >=22 while CI runs Node 20. The
runTests API is unchanged.

Verified locally: version resolves and VS Code downloads successfully
(the prior failure point); compile passes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: vicperdana