[Blank Canvas Blocks] Add block patterns

[jffng]

Evaluate each of the block patterns available in Blank Canvas and determine which can be made available in Blank Canvas Blocks without adding any additional custom CSS to the theme.

[kjellr]

⚠️ EDIT: I left more up-to-date comments in the PR: #3514 (comment).

I took a look at the existing Blank Canvas patterns, and they're looking way off at this point:

A few obvious bugs:

• Full-width doesn't go full width, there are other content-width errors throughout.
• The page title is present. (Should I be switching to a different template here? Not sure how that is supposed to work)
• The theme colors used in the original theme don't match up with those in BCB. This makes some text unreadable, and changes a bunch of the button colors. (Might make sense to hardcode the colors in the patterns instead?)
• The spacing between blocks is different or wrong.
• Font weights don't match.

Here's the test content taken right from the original Blank Canvas.

I'm going to hold off on testing again until this is in a closer state, but please let me know if you have any design questions about that stuff.

Blank Canvas	Blank Canvas Blocks

[MaggieCabrera]

Closed via #3514