When asserting microtime output as a number, make it a number

microtime is by default a string. Doing a greater then or less than check of that string is a bad idea since it uses the first part (the micro part of microtime) rather then the actual time. This adds a helper to convert microtime output into a float which we can then use to properly compare the output of microtime.

This fixes an intermittent test failure.

fixes #30336


Built from https://develop.svn.wordpress.org/trunk@30337


git-svn-id: http://core.svn.wordpress.org/trunk@30336 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Introduce Distraction-Free Writing v2, a re-think of DFW that uses the main editor instance

* the "DFW" button is now an auto/off toggle
* defaulting to auto during beta, decide later for release
* "auto" means that DFW gets enabled as you start typing in editor
* tabbing and mousing out will bring the full interface back
* there is a slight grace period during which your mouse can quickly return

Feature plugin work happened here: https://github.com/avryl/focus

props avryl, azaozz, Michael Arestad
fixes #29806
Built from https://develop.svn.wordpress.org/trunk@30338


git-svn-id: http://core.svn.wordpress.org/trunk@30337 1a063a9b-81f0-0310-95a4-ce76da25c4cd