Resolve "Visual regression in 12.0: line numbers not lining up in file view"

What does this MR do?

Align line numbers & code when browser font size >16px.
Min/line height in ems instead of px

1. Previous line-height was 19px, which was approx 1.5x the font size (exact would be 18.9px)
2. Font size comes from 90% of our 14px base font size (12.6px)
3. Min height with ems needed for empty lines

Before:

After:

Closes #63010 (closed)