Preformatted block: add line-height control option

[sabernhardt]

What problem does this address?

As @noisysocks noted on Trac ticket 48402:
With default pre element styles in the (Twenty Twenty) theme, "the line height in a Preformatted block is so large that it renders the block impractical for things such as ASCII art and diagrams."

Any theme can specify a large line-height, so having an option to reduce that on preformatted blocks would help. Then any adjustments for ASCII art do not affect other pre blocks that benefit from a larger line-height, such as Verse and Code.

Screenshot from the Trac ticket:

What is your proposed solution?

The Preformatted block could have the same line-height control currently available for Paragraph blocks (when opted in).

[noisysocks]

@nosolosw: Is line-height something that can be adjusted in global styles?

[oandregal]

Yup, absolutely. Any block can declare support for it and then themes can target that style.

[noisysocks]

Awesome. Sounds like we just need to set supports.lineHeight to true in the Preformatted block, then.

This value signals that a block supports the line-height CSS style property. When it does, the block editor will show an UI control for the user to set its value if the theme declares support.

[Mamaduka]

Fixed via #34064.