fix: clear parent change listener before disposeContext in ScopedContextKeyService

[maruthang]

Fixes #307067

Summary

• ScopedContextKeyService.dispose() now calls this._parentChangeListener.clear() before this._parent.disposeContext(this._myContextId)
• Previously, the parent emitter listener could still fire during disposal if a context change occurred between the start of dispose() and super.dispose() being called, contributing to the listener leak

Test plan

• Create many scoped context key service instances and dispose them — the "potential listener LEAK detected" warning should no longer appear in the console

[Copilot]

Pull request overview

This PR fixes a potential listener leak in the platform ContextKeyService by ensuring ScopedContextKeyService stops forwarding parent context-change events before tearing down its scoped context.

Changes:

• Clear the scoped service’s parent onDidChangeContext listener at the start of ScopedContextKeyService.dispose().
• Dispose the scoped context (disposeContext) only after detaching from parent events, preventing late event forwarding during teardown.

Show a summary per file

File	Description
src/vs/platform/contextkey/browser/contextKeyService.ts	Adjusts ScopedContextKeyService.dispose() ordering to detach parent listener before disposing scoped context, addressing listener leak warnings.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1

[Copilot]

This disposal-order fix would be safer with a regression test. There are existing unit tests for ContextKeyService, but none appear to cover that a disposed scoped service stops forwarding parent onDidChangeContext events (and doesn’t contribute to listener leak warnings). Consider adding a test that creates many scoped services, disposes them, then mutates the parent context and asserts no child change events fire / no listeners remain attached.

Suggested change

	this._parent.disposeContext(this._myContextId);
	this._domNode.removeAttribute(KEYBINDING_CONTEXT_ATTR);
	super.dispose();
	try {
	this._parent.disposeContext(this._myContextId);
	this._domNode.removeAttribute(KEYBINDING_CONTEXT_ATTR);
	} finally {
	super.dispose();
	}