API: support call stacks in TestMessages

[connor4312]

Currently, messages that are shown when tests fail can only be shown at a single Location. Often (connor4312/nodejs-testing#37, #214287 (comment), among others) folks want to see the full call stack of the test failure.

I propose some API to add this information:

declare module 'vscode' {
	export class TestMessage2 extends TestMessage {
		/**
		 * The stack trace associated with the message or failure.
		 */
		stackTrace?: TestMessageStackFrame[];
	}

	export class TestMessageStackFrame {
		/**
		 * The location of this stack frame. This should be provided as a URI if the
		 * location of the call frame can be accessed by the editor.
		 */
		file?: Uri;

		/**
		 * Position of the stack frame within the file.
		 */
		position?: Position;

		/**
		 * The name of the stack frame, typically a method or function name.
		 */
		label: string;

		/**
		 * @param label The name of the stack frame
		 * @param file The file URI of the stack frame
		 * @param position The position of the stack frame within the file
		 */
		constructor(label: string, file?: Uri, position?: Position);
	}
}

[timheuer]

@connor4312 does this track that not only the stack but stack + any stdout would show in same UX? /cc @peterwald

[connor4312]

Yes, output is already trackable and associable to a test case via the run.appendOutput API

[peterwald]

We are using appendOutput() to record all stdout written by tests. In addition, the test.fail() is used to record the failure message and stack for each test failure.