Add basic unit tests for `is_plugin_active()` and `is_plugin_inactive()`.

Props voldemortensen.
Fixes #30489.
Built from https://develop.svn.wordpress.org/trunk@30557


git-svn-id: http://core.svn.wordpress.org/trunk@30546 1a063a9b-81f0-0310-95a4-ce76da25c4cd
TinyMCE: use the actual image node when calculating the position of the toolbar. Fixes a bug in old IE. See #30147.
Built from https://develop.svn.wordpress.org/trunk@30558


git-svn-id: http://core.svn.wordpress.org/trunk@30547 1a063a9b-81f0-0310-95a4-ce76da25c4cd