Add basic unit tests for `is_plugin_active_for_network()`

Props rodrigosprimo
Fixes #30491


git-svn-id: https://develop.svn.wordpress.org/trunk@30559 602fd350-edb4-49c9-b593-d223f7449a82
TinyMCE: don't hide the image toolbar when the iframe window fires onresize. There is a bug in several browsers that triggers onresize when a tooltip is shown, only in RTL mode. Also use better variable name. Fixes #30147.

git-svn-id: https://develop.svn.wordpress.org/trunk@30560 602fd350-edb4-49c9-b593-d223f7449a82