selection-text-shadow-*

These can all be collapsed to one test.

http://www.gtalbot.org/BrowserBugsSection/CSS4Pseudo/selection-text-shadow-015.html
does all 4 directions

We don't need a separate test for each possible offset!

Chromium 78 (stable version) and Chromium 81 (latest build) "struggle" with selection-text-shadow-014.html
Try this:
Double-click each word or triple-click or mousedrag the blue words in
http://www.gtalbot.org/BrowserBugsSection/CSS4Pseudo/selection-text-shadow-014.html
and the red text shadow will not disappear. Though, the failures are erratic, not easy to reproduce consistently ...

If you're concerned about errors in paint invalidation,
place offsets in all four directions. Also, I think an 0.5em
offset should be sufficient here: multiple copies of the
text is a bit confusing.

If the test as designed is passed, then there is only 1 "Text sample" readable, viewable and it must be green.

I will use a 0.5em offset for each direction in
selection-text-shadow-015 .

I will remove
selection-text-shadow-011
selection-text-shadow-012
selection-text-shadow-013
selection-text-shadow-014 .

Lastly, I suggest using the text “Selected Text” instead of “Sample Text”, since it's a little more helpful to the tester. :)

I will replace "Sample text" with "Selected Text".

http://www.gtalbot.org/BrowserBugsSection/CSS4Pseudo/selection-text-shadow-015-new.html

http://www.gtalbot.org/BrowserBugsSection/CSS4Pseudo/selection-text-shadow-015-new-ref.html

I will create another Pull Request and remove the "-new" from filenames.

I am closing this pull request and inviting you in #20802
which addresses your feedback in this PR ... My weak current github "skills" prevent me from doing this in here... :(