This only paints text in input fields. Selection and cursor are still
not painted.
In addition to adding this feature, the change also updates the
user-agent.css with the latest from the HTML specification. Extra
padding and extraneous settings (such as a bogus line-height and
min-height) are also removed from servo.css. This leads to some new
passes.
There are some new passes, this introduces failures as inserting text
reveals issues that were hidden before. Notably:
- failures in `/html/editing/editing-0/spelling-and-grammar-checking/`:
We do not support spell-checking.
- Most of the rest of the new failures are missing features of input
boxes that are also missing in legacy layout.
