Editing peformance is rough for large lists

**Describe the bug**

When authoring in a large list, there are long pauses between keystrokes.

**To Reproduce**

1. Go to https://www.netlifycms.org/admin/#/collections/updates/entries/releases
2. Edit one of the list items

**Expected behavior**

Updates should be snappy.

**Applicable Versions:**
CMS 2.10.31

**Additional context**

This is a long known issue, just needed to be documented. `shouldComponentUpdate` is currently set to always update on lists because the list widget doesn't know if it's children require updates from whatever state change is coming down.

I'm certain we can be smarter about this logic. If we can get a quick easy win, let's at least prioritize it. If it's likely to be a bigger lift, let's just get some thoughts down and prioritize later.

An improvement here will likely improve perf across the editor, or at least pave the way for general perf improvement.