Build/Tests Tools: Add unit tests for Gallery blocks.
Introduces unit tests for the following blocks
- Gallery block with caption
- Gallery block, deprecations 1 thru 7
Updates the unit tests for the following blocks to match the counterparts stored in the Gutenberg repository:
- Gallery block
- Gallery block with columns
Modifies Tests_Blocks_Render::test_do_block_output() to ignore white space at the end of lines to account for whitespace equivalence in HTML.
Props peterwilsoncc, isabel_brison, gziolo.
Fixes #55571.