🐛 Fix repeated CWD entries when creating new terminal in multi-root workspace

[babakks]

This PR fixes #153125

Tests to verify the correct dropping of repeated CWDs were added.

In the screenshot:

• a multi-root directory workspace with four roots is activated. You can clone the test workspace from babakks/vscode-test-multi-root-workspace.
• Overridden in dir-a/.vscode/settings.json, the CWD for dir-a is set to ../dir-b. Due to this, dir-a was dropped from the picker list.
• Overridden in dir-d/.vscode/settings.json, the CWD for dir-d is set to .. (parent directory). Since just showing dir-d and its path in the picker makes no sense to the user, it is shown with an "(Overridden)" indicator followed by the actual CWD to clarify the user.

Since the PICK_WORKSPACE_FOLDER_COMMAND is a general-purpose functionality which is used in different places, I opted to locally implement the picker within the terminal module.

@Tyriar Although the fix seems to work, there are two other instances in the codebase where the CWD picker does not respect the terminal.integrated.cwd parameter. Please check these and tell me whether to fix them.

terminalActions.ts#L62:

case 'workspaceRoot':
	if (folders !== undefined && commandService !== undefined) {
		if (folders.length === 1) {
			return folders[0].uri;
		} else if (folders.length > 1) {
			// Only choose a path when there's more than 1 folder
			const options: IPickOptions<IQuickPickItem> = {
				placeHolder: localize('workbench.action.terminal.newWorkspacePlaceholder', "Select current working directory for new terminal")
			};
			const workspace = await commandService.executeCommand(PICK_WORKSPACE_FOLDER_COMMAND_ID, [options]);
			if (!workspace) {
				// Don't split the instance if the workspace picker was canceled
				return undefined;
			}
			return Promise.resolve(workspace.uri);
		}
	}
	return '';

terminalActions.ts#L2453:

const folders = workspaceContextService.getWorkspace().folders;
if (folders.length > 1) {
	// multi-root workspace, create root picker
	const options: IPickOptions<IQuickPickItem> = {
		placeHolder: localize('workbench.action.terminal.newWorkspacePlaceholder', "Select current working directory for new terminal")
	};
	const workspace = await commandService.executeCommand(PICK_WORKSPACE_FOLDER_COMMAND_ID, [options]);
	if (!workspace) {
		// Don't create the instance if the workspace picker was canceled
		return;
	}
	cwd = workspace.uri;
}

[Tyriar]

Works well 👍 sorry about the delay getting to this