layout: Support wavy and double for text-decoration-line (#37079)

- Add support for `text-decoration-line: double`: Line drawing is done
similar to how it works in Firefox and Chromium. A gap of half of line
thickness is added between each line.
- Fix support for `text-decoration-line: wavy`: Wavy lines rectangles
were not calcualted properly, which meant they were rendered as solid
lines. Now the amplitude of the wave is 1.5 times line thickness.

Testing: A manual test is updated `tests/html/text_deco_simple.html`
to cover more cases. In general, rendering of text-decorations is
difficult
to test via reftesting.
Fixes #17887.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/layout/display_list/conversions.rs

@@ -125,11 +125,15 @@ impl ToWebRender for ComputedTextDecorationStyle {
     type Type = LineStyle;
     fn to_webrender(&self) -> Self::Type {
         match *self {
-            ComputedTextDecorationStyle::Solid => LineStyle::Solid,
+            ComputedTextDecorationStyle::Solid | ComputedTextDecorationStyle::Double => {
+                LineStyle::Solid
+            },
             ComputedTextDecorationStyle::Dotted => LineStyle::Dotted,
             ComputedTextDecorationStyle::Dashed => LineStyle::Dashed,
             ComputedTextDecorationStyle::Wavy => LineStyle::Wavy,
-            _ => LineStyle::Solid,
+            ComputedTextDecorationStyle::MozNone => {
+                unreachable!("Should never try to draw a moz-none text decoration")
+            },
         }
     }
 }