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/flow/inline/construct.rs

@@ -283,6 +283,7 @@ impl InlineFormattingContextBuilder {
             layout_context,
             text_decoration_line,
             has_first_formatted_line,
+            /* is_single_line_text_input = */ false,
         )
     }
 
@@ -292,6 +293,7 @@ impl InlineFormattingContextBuilder {
         layout_context: &LayoutContext,
         text_decoration_line: TextDecorationLine,
         has_first_formatted_line: bool,
+        is_single_line_text_input: bool,
     ) -> Option<InlineFormattingContext> {
         if self.is_empty() {
             return None;
@@ -305,6 +307,7 @@ impl InlineFormattingContextBuilder {
             layout_context,
             text_decoration_line,
             has_first_formatted_line,
+            is_single_line_text_input,
         ))
     }
 }