Allow extensions to access all terminals

[Tyriar]

New proposed APIs:

export namespace window {
	/**
	 * The currently active terminals or an empty array.
	 *
	 * @readonly
	 */
	export let terminals: Terminal[];

	/**
	 * An [event](#Event) which fires when a terminal has been created, either through the
	 * [createTerminal](#window.createTerminal) API or commands.
	 */
	export const onDidOpenTerminal: Event<Terminal>;
}

Changes to existing behavior:

• Terminal.name and Terminal.processId can be accessed on a disposed terminal

See usage example at https://github.com/Microsoft/vscode-extension-samples/blob/master/terminal-sample/src/extension.ts

Fixes #13267
Part of #46192

/cc @dbaeumer @weinand @IlyaBiryukov @alpaix

[jrieken]

Think about a TerminalOpenEvent so that you a chance of adding more stuff in the future..

[jrieken]

Then, should open come with close?

[Tyriar]

onDidCloseTerminal already exists as an Event<Terminal>:

https://github.com/Microsoft/vscode/blob/da9720b39b1a912ce8009587731d824a890797ad/src/vs/vscode.d.ts#L4905-L4908

[jrieken]

missed that 🤦‍♂️

[Tyriar]

Different file 😉