Add docs to some functions in event.ts
Add docs to some functions in event.ts

Part of #163572

microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode