Use DisposableMap for session listener lifecycle in FocusSessionActionViewItem

[Copilot]

Addresses review feedback from #293155 to use DisposableMap for tracking debug session listeners, preventing leaks when the component is disposed while sessions are still active.

Changes

Replaced array-based listener tracking with DisposableMap pattern:

• Session listeners now tracked in DisposableMap<string, DisposableStore> registered with component lifecycle
• Listeners properly disposed on session end and component disposal
• Follows pattern from loadedScriptsView.ts:545-591

Simplified disposal logic:

• Removed redundant onDidEndAdapter cleanup (sessions always fire onDidEndSession)
• Added defensive cleanup in registerSessionListeners to handle potential duplicate calls

Merged main branch:

• Merged latest changes from main branch
• Resolved conflict by keeping the improved DisposableMap implementation over the old array-based pattern

// Before: listeners leak when component disposes with active sessions
const sessionListeners: IDisposable[] = [];
sessionListeners.push(session.onDidChangeName(() => this.update()));
sessionListeners.push(session.onDidEndAdapter(() => dispose(sessionListeners)));

// After: proper lifecycle management
const sessionListeners = this._register(new DisposableMap<string, DisposableStore>());
const store = new DisposableStore();
sessionListeners.set(session.getId(), store);
store.add(session.onDidChangeName(() => this.update()));
// Auto-disposed when component or session ends

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[jrieken]

@copilot merge main and fix conflicts

[Copilot]

@copilot merge main and fix conflicts

Merged main in 4d70e4c. The conflict in debugActionViewItems.ts was resolved by keeping our DisposableMap implementation (our changes replaced the old array-based pattern that was present in main).