Feature: Implement lint rule to eliminate accidental nested updates

Description

Nested updates are never a good idea, so if we find a $function (or a registerCommand) that has an embedded editor.update we should rewrite it to remove the editor.update. As a companion to this we could add a $defer or something like that which could be used to provide explicit nested update semantics but I doubt we'll actually find any use case for it.

Impact

Bugs will be avoided, code will be easier to test when the effects of updates happen in a sensible order. Nobody really wants to reason about code that looks like this:

editor.dispatchCommand(COMMAND_A, undefined);
editor.update(() => $b());
editor.dispatchCommand(COMMAND_C, undefined);

that will either execute in A, B, C or A, C, B order depending on the context of whether this is called inside of an editor.update (or command listener) or not.

RE #7039 #7037 for recent examples