Provide 3-pane layout where "Local" and "Remote" are shown w/o diffs?

[eacousineau]

Which problem is your feature request related to, if any?

Layouts

Solution you'd like

An extra layout option, if possible; similar to 3DiffTo* flavors, but only show diff in one pane ("Merged"), and base changes in other ("Local", "Remote").

Perhaps named 3LocalMergedRemote?

From looking at code, I think it'd be something like changing this to use type: LayoutElementType.normalEditor?

vscode-as-git-mergetool/src/layouters/threeDiffToBaseLayouter.ts

Lines 43 to 52 in de60bc0

	groups: [
	{
	size: leftSize,
	type: LayoutElementType.diffEditor,
	oldUri: diffedURIs.base,
	newUri: diffedURIs.local,
	title: "(1) Current changes on base",
	save: false,
	notFocussable: zoom === Zoom.right,
	},

Description of alternatives you've considered

I've briefly tried out existing 3DiffTo* layouts, but get confused when all panes show diffs.

Additional context

I believe this is similar to how Meld works.