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.

tests/wpt/mozilla/meta/MANIFEST.json

@@ -3473,7 +3473,7 @@
      ]
     ],
     "input_line_height.html": [
-     "1de07c88ae2092e2e9885d30e2001e9fe09ca8b3",
+     "f1c1d742000a6c4c11d40806e07aeba502141368",
      [
       null,
       [
@@ -6547,7 +6547,7 @@
      ]
     ],
     "textarea_space_calculation.html": [
-     "20945e971b543cbc11741863314ccf3595654e80",
+     "ee5ea7b1c01f5a11188bc50eca3a60ea2c15edf2",
      [
       null,
       [
@@ -9115,7 +9115,7 @@
      []
     ],
     "input_line_height_ref.html": [
-     "16d4fd99712bd1d21cc8320f2e273a867f3fb807",
+     "f29e061cc35625fa039473e702f78dbc5a7d9c14",
      []
     ],
     "input_placeholder_ref.html": [
@@ -10073,7 +10073,7 @@
      []
     ],
     "textarea_space_calculation-ref.html": [
-     "b777beb062b67a51c1efdfe4afa55568fd3724e6",
+     "56abdf23c8f88a9f236d54ef798734becc372027",
      []
     ],
     "transform_3d_from_outside_viewport_ref.html": [