This converts the TextLayout algorithm from handling just words to
handling blocks of strings. With this model, whitespace is preserved
and inserted as-is, rather than being eaten and then replaced with a
single space (or none, if the whitespace was at the start of the word).
Closes#9032.
This class now contains all the fun bits about laying out text in a
rect. It will handle line wrapping at a certain width, cutting off lines
that don't fit the given rect, and handling text elision.
Painter::draw_text now internally uses this.
Future work here would be not laying out text twice (once actually
preparing the lines to be rendered and once to get the bounding box),
and possibly adding left elision if necessary.
Additionally, this commit makes the Utf32View versions of
Painter::draw_text convert to Utf8View internally. The intention is to
completely remove those versions, but they're kept at the moment to keep
the scope of this PR small.
