[EuiContextMenu] Fix post-transition unclickable menu items

[thompsongl]

Summary

Fixes #3547, in which menu items in an EuiContextMenuPanel would become unclickable after animating in. The problem was caused by the applied animation class (e.g., .euiContextMenuPanel-txOutRight) that sets pointer-events: none; not being removed after the animation end.

This appeared only in Chromium browsers and was likely spurred on by a recent (unknown) change that resulted in a setState race condition.

The solution here is to bypass the offending state update by removing it entirely. The isTransitioning state flag was nothing more than an analog for the existence of the transitionType prop provided by the parent component and updated on the same events. Replacing isTransitioning and its setState methods with a truthy prop check simplifies logic without changing behavior.

Also fixed a bug in the docs that was causing prop type warnings in dev mode.

Checklist

- [ ] Check against all themes for compatibility in both light and dark modes
- [ ] Checked in mobile
- [ ] Checked in IE11 and Firefox
- [ ] Props have proper autodocs
- [ ] Added documentation

• Checked Code Sandbox works for the any docs examples

- [ ] Added or updated jest tests

• Checked for breaking changes and labeled appropriately

- [ ] Checked for accessibility including keyboard-only and screenreader modes

• A changelog entry exists and is marked appropriately

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3656/

[snide]

Tested this functionally and browsed the code. Looks to have fixed the problem. Simple fix! Bet that was hard to track down.

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3656/