layout: Add very basic support for showing text in input boxes (#32365)

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.

components/layout_2020/flexbox/construct.rs

@@ -159,7 +159,8 @@ where
                     let Some(inline_formatting_context) = inline_formatting_context_builder.finish(
                         self.context,
                         self.text_decoration_line,
-                        true, /* has_first_formatted_line */
+                        true,  /* has_first_formatted_line */
+                        false, /* is_single_line_text_box */
                     ) else {
                         return None;
                     };