Uppercase strings rather than chars for small-caps

[SimonSapin]

Currently, font-variant: small-caps is implemented with synthesized small caps: transform the text to upper case and use a smaller font size. gfx::font::glyph_index contains code like codepoint.to_uppercase().next().unwrap() to find the upper case of a single code point. .next().unwrap() takes the first char in the iterator returned by char::to_uppercase and drops the rest.

This is OK at the moment since the iterator always of length 1. But in the future, it will do complex case mapping and may yield more than one char, and the rest should not be dropped. See #23126

The small-caps implementation should probably use str::to_uppercase earlier in the code, before considering individual chars.

[SimonSapin]

I just realized it’s not as easy as upper-casing entire text nodes, we only want to reduce the font size of things that were previously lower-case.

[jdm]

@SimonSapin Wrong repo?

[SimonSapin]

Oops! Yes, sorry.