Implement shouldPersist for all terminals processes

shouldPersist was not being set on RemoteTerminalProcess, causing reconnect
to fail for all remote terminals. The fix was to push the persistent logic
up to where the process gets created in TerminalProcessManager just like is
done with local processes. The property was made non-optional to prevent
this sort of thing happening again.

Part of #117896

src/vs/workbench/api/common/extHostTerminalService.ts

@@ -185,6 +185,7 @@ export class ExtHostTerminal {
 
 export class ExtHostPseudoterminal implements ITerminalChildProcess {
 	readonly id = 0;
+	readonly shouldPersist = false;
 
 	private readonly _onProcessData = new Emitter<string>();
 	public readonly onProcessData: Event<string> = this._onProcessData.event;