Previously, when a @font-face font finished loading, we would clear the
entire computed font cache and invalidate style for the whole document.
This was overly conservative since most elements don't use the newly
loaded font. We now take a targeted approach inspired by Firefox:
1. Only clear cache entries that reference the loaded font family
2. Walk the DOM tree (including shadow trees) and only invalidate
elements whose font-family property (or pseudo-elements' font-family)
actually references the loaded font
This significantly reduces style invalidation work on pages with many
elements but only some using custom fonts.
This method was only called when `font_matching_algorithm` failed to
match a font (i.e. there are no fonts with a matching family name) in
which case this method would also fail to match a font.
Previously we wouldn't respect font-variation-settings for fonts matched
through `font_matching_algorithm` (i.e. any fonts which didn't have an
exact loaded match).
The `VectorFont` type was renamed to `Typeface` in d5926a3 but this
member variable was never updated.
The getter for this was also unused so has been removed
When rendering text, if none of the fonts in the cascade list contain a
glyph for a given code point, we now query Skia's font manager to find
a system font that can render it.
Computing the font for an element in `compute_font` is premature since
we are yet to apply animated properties - instead we should compute the
value on the fly (with a cache to avoid unnecessary work) to ensure we
are respecting the latest values
Font computation and loading is distinct enough from style computation
that it makes more sense to have this in it's own class.
This will be useful later when we move the font loading process to
`ComputedProperties` in order to respect animated values.
