Diff styles for moving paragraphs and empty lines
- Fix styling of empty lines - cover full width
- Disable the pseudo element shipped in core
- Move styles from mobile.special.mobilediff.styles into mediawiki.diff.styles
since the latter is always present, the former isn't if MobileFrontend is not
available.
Bug: T242310
Bug: T243235
Change-Id: Ic7d12fe890622e7b3ccc7bc56765f505ac0ab651