R1:8cdafb003250

Allow users to set a line-height in their monospaced font preference

Summary: Ref T10959. This does not fix the problem because the `.differential-diff td` rule is still stronger, but it does let you choose a more compact or breezy style for remarkup blocks and pastes.

Test Plan:
- Set font to `24px / 48px impact`.
- Viewed a paste, saw lovely readable text.
- Viewed an inline code block which was very easy on the eyes.

{F1310420}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10959…