Improve theme.json test failure messages by pretty printing css for a…

… more accurate diff (WordPress#64077)

* Add basic formatting function and apply to one test

WIP

Add comment

* Add assertSameCSS expectation which outputs pretty printed test failure along with raw css for updating the test

Update accidentally committed test failure

Fix expected,actual order and minimize diff

Fix - make sure the actual is output in addition to the pretty printed failure, not the expected

Update test expectation so test passes

Revert "Update test expectation so test passes"

This reverts commit c9f655a.

Update test expectation so test passes

* Convert comment to docblock

----

Co-authored-by: talldan <[email protected]>
Co-authored-by: andrewserong <[email protected]>
Co-authored-by: ramonjd <[email protected]>