replace requestAnimationFrame approach with vanilla css. This has the benefit of being simpler and handling multi-line text much better.
bump the version number
closes MAT-1134
test plan:
in the rce have enough content so you have to scroll.
change some text color to have inadequate contrast, including some multi-line stuff
add an image and leave the alt text the file name.
open the a11y checker
expect a black-ish box around each violation
expect it to scroll with the rce content and/or the page
expect it to scroll out of view when the tinymce menubar+toolbar header gets position:fixed at the top of the page and the rce content scrolls behind it
expect the indicator box to disappear when you close the a11y-checker
expect it to behave in the transition in and out of fullscreen
closes MAT-1134
test plan: