fix: memory leak main thread terminal service

[SimonSiefke]

Fixes a memory leak in mainThreadTerminalService.

Details

Registering a terminal completion provider happens through this code:

private readonly _completionProviders = new Map<string, IDisposable>();

public $registerCompletionProvider(id: string, extensionIdentifier: string, ...triggerCharacters: string[]): void {
	this._completionProviders.set(id, this._terminalCompletionService.registerTerminalCompletionProvider(/*...*/)

When a completion provider with the same id gets registered again, instead of replacing the completion provider, another one gets created. And the previous completionProviders[id] Disposable kind of gets unreferenced.

Fix

The fix uses a DisposableMap so that at most one completion provider gets registered with the same id. When another completion provider with the same id gets registered, the previous registration will be disposed.

Before

When debugging a python file 37 times, the number of TerminalCompletionService.registerTerminalCompletionProvider functions seems to grow by one each time:

After

When debugging a python file 37 times, while the number of some functions still seems to grow, the number of TerminalCompletionService.registerTerminalCompletionProvider functions now stays constant: