Add argument parsing, suite filtering, and grep support to integration test scripts (#305837)

* Add argument parsing, suite filtering, and grep support to integration test scripts

- Add --run, --runGlob, --grep, --suite, and --help argument parsing
- --suite selects extension host test suites (comma-separated, glob patterns)
- --grep forwards test name filter to all runners via MOCHA_GREP env var
- Validate --suite filter matches at least one known suite
- Add MOCHA_GREP support to testrunner.js, CSS and HTML test runners
- Seed user settings to suppress dock bounce notifications
- Always apply *.integrationTest.js glob for node.js tests
- Add integration-tests skill documentation

* Address Copilot review feedback

- Quote cd $ROOT, rm -rf $VSCODEUSERDATADIR, rmdir %VSCODEUSERDATADIR%
- Quote --runGlob pattern to prevent premature glob expansion
- Use GREP_ARGS array for safe grep forwarding in .sh
- Use conditional call with proper quoting for grep in .bat
- Deduplicate suite list into KNOWN_SUITES variable
- Remove unused EXTRA_ARGS and ARGS variables from .bat

* Fix Windows CI: remove unnecessary enabledelayedexpansion

The original script used plain 'setlocal'. Adding 'enabledelayedexpansion'
may affect path resolution behavior on Windows CI. Since no delayed
expansion (\!var\!) syntax is used, revert to the original 'setlocal'.

* Fix Windows CI: capture %~dp0 before call :label corrupts it

In Windows batch, 'call :label' can change what %~dp0 resolves to.
Our should_run_suite subroutine uses 'call :should_run_suite', which
caused %~dp0 to resolve to the wrong directory for extension paths
that appear after the subroutine call. Capture the script directory
once at startup into %SCRIPT_DIR% and use it everywhere.