Fix restartLanguageServer command not found in command palette (#22045)

[arymaheshwari]

Fixes #22045

Problem

The python.analysis.restartLanguageServer command was previously owned by Pylance and was removed from it. The vscode-python extension registered the command handler inside individual manager constructors (NodeLanguageServerManager, JediLanguageServerManager), so it was only available when Pylance or Jedi was active — never when LanguageServerType.None was in use.

Additionally, LanguageServerWatcher.restartLanguageServers() had an async/forEach bug that silently discarded all awaits, and was never called from anywhere.

Changes

• watcher.ts: Register RestartLS command in register() so it is always active; fix restartLanguageServers() with for...of and correct URI handling
• node/manager.ts: Remove static commandDispose and command registration from constructor
• jedi/manager.ts: Same cleanup
• watcher.unit.test.ts: Fix disposable count assertions, fix ICommandManager mocks, add new test for restart command handler

Testing

All 24 language server watcher unit tests pass (npm run test:unittests). Zero TypeScript errors (tsc --noEmit)

[arymaheshwari]

@microsoft-github-policy-service agree

[eleanorjboyd]

@rchiodo @bschnurr @StellaHuang95 could I get a review of this to confirm this is the desired behavior for this interaction

[eleanorjboyd]

The implementation appears to support Pylance through PylanceLSExtensionManager/NodeLanguageServerProxy, without requiring Pylance itself to register this command. However, the new test uses LanguageServerType.None and stubs NoneLSExtensionManager, so it only verifies that the command is registered and routed through the watcher when no language server is active. It does not verify the behavior this issue is primarily concerned with: that invoking the command actually stops and restarts Pylance. Could we add a Pylance-specific test that asserts the Pylance manager/client is stopped and started?