This adds snapshot tests for indentation issues described in:

• Bad indentation after curly braces #1683
• https://github.com/posit-dev/positron-beta/discussions/46
• R: indentation issue with finished pipes #1727
• Ark: Indentation after a single line loop #1880
• Pipelines identation on R files #1316
• Which of this language configuration sparks joy? #1655 (comment)

Closes #1694.

I initially tried to import the indentation test cases from ESS (https://github.com/emacs-ess/ESS/blob/master/test/styles/RStudio-.R). However those tests assume you can do something like the reindent lines action.

• Reindent lines doesn't work here because it only uses regular indentation rules without on-enter rules, which isn't consistent with what happens when the user types Enter.

• Pasting with auto-indent doesn't work either because it doesn't match the behaviour the user would see when typing the code manually. For instance, typing a closing delimiter like ) triggers a "matching indent", see

  positron/src/vs/editor/common/cursor/cursorTypeOperations.ts

  Lines 947 to 963 in 06743ca

  	if (!isDoingComposition && this._isAutoIndentType(config, model, selections)) {
  	const commands: Array<ICommand | null> = [];
  	let autoIndentFails = false;
  	for (let i = 0, len = selections.length; i < len; i++) {
  	commands[i] = this._runAutoIndentType(config, model, selections[i], ch);
  	if (!commands[i]) {
  	autoIndentFails = true;
  	break;
  	}
  	}
  	if (!autoIndentFails) {
  	return new EditOperationResult(EditOperationType.TypingOther, commands, {
  	shouldPushStackElementBefore: true,
  	shouldPushStackElementAfter: false,
  	});
  	}
  	}

  . This special dedenting behaviour doesn't happen on paste.

• Typing the whole file in a loop one character at a time doesn't work either, because typing an opening delimiter like { auto-closes it, which corrupts the snapshots. Disabling auto-closing doesn't help because without the closing delimiters, we can't reproduce some of the regexp rules sensitive to those delimiters.

After struggling a while I gave up on this approach. I think we need to test only one action per snapshot case. This is what is implemented in the indentation-cases.R (inputs) and indentation-snapshots.R (outputs) files. These contain a list of fenced snapshots with a special marker indicating the cursor position. The snapshots are inserted in an editor and a newline is typed at the cursor. The result is pushed to the snapshot files.

The infrastructure for this is based on the Typescript tests for indentation that @juliasilge discovered: https://github.com/posit-dev/positron/blob/main/extensions/typescript-language-features/src/test/unit/onEnter.test.ts#L36C1-L36C1. These are disabled because of intermittent failures on Windows so we'll have to watch out for that.

I've added a VS Code workspace inside the test folder to hold overridden settings. That's a bit of a heavier setup that I'd like but I don't think it's possible to create a virtual context where we could override settings for unit tests?

In terms of workflow these snapshots are in line with the way testthat handled snapshots pre edition 3. The snapshots are always regeneratedv If they don't match this is an error, but rerunning the test will no longer fail as the snapshots have been updated. The differences should be inspected with git and either accepted if the new output is correct, or discarded if it's not.