[Widget Performance] Slowdown on data-heavy, nested-list collection pages

[geotrev]

Describe the bug
I'm using several list widget + string widget entries in an object widget. I have about 100 items spread across multiple object widgets, and the lag is very noticeable.

To make this example more clear, I created an isolated example here. add a couple items to the new config on that branch and it should exponentially increase the lag of typing, expanding panels, etc.

To Reproduce

1. Checkout master and add in the config below in CMS configuration to dev-test/config.yml.
2. Bootstrap, kick off the server and go to the kitchen sink example
3. Try to navigate collection: open collapsed sections, type in fields, add items, etc.

Behavior
Expected: UI responds quickly to all actions/events (clicking, typing).
Actual: UI responds quite slowly. Sometimes up to a full second just from typing.

Applicable Versions:

• Netlify CMS version: 2.10.192
• Git provider: Github
• OS: Windows 10.0.19044
• Browser version: Firefox 105.0.1 (64 bit) + Chrome 105.0.5195.127 (Official Build) (64-bit)
• Node.JS version: v16.17.1 (npm v8.15.0) (on netlify server)

CMS configuration:

Link to config

Additional context

This slowdown happens in any environment/browser combo, I'm noticing. Even on very simple lists with less than 10 items, but a handful of fields in each.

[geotrev]

Per the OP, here's what I mean by visible DOM even when lists are collapsed (grayed out nodes are not visible). These nodes are receiving updates for each render (opening a top level list causes updates to visually hidden child lists).

[geotrev]

Closing this and posted PR suggestion on #3415.