Fix loading raw data from .ttc files on macos (#38753)

# Objective

Ensure that functionality which uses the raw font data (such as
rendering text to canvas) works correctly on macOS when the specified
font is a system font that lives in an OpenType Collection (`.ttc`)
file.

## Changes made

- The `read_data_from_file` in each backend now returns a `index: u32`
in addition to `data: Vec<u8>`
- The `data` field on the `Font` type has been renamed to `raw` and the
`data` method on the `Font` type has been renamed to `raw_font`. This
allows the index to be cached as computing is moderately expensive on
macOS (on the order of 100 microseconds).
- Both of the above now store/return a `struct RawFont` instead of a
`FontData` where `RawFont` is defined as `struct RawFont { data:
FontData, index: u32 }`.
- The users of the `data` method have been updated to use the cached
index from `data` rather than calling `.index()` each time.

---------

Signed-off-by: Nico Burns <nico@nicoburns.com>

components/canvas/peniko_conversions.rs

@@ -9,6 +9,13 @@ use style::color::AbsoluteColor;
 use crate::backend::Convert;
 use crate::canvas_data::Filter;
 
+impl Convert<peniko::Font> for fonts::FontDataAndIndex {
+    fn convert(self) -> peniko::Font {
+        use std::sync::Arc;
+        peniko::Font::new(peniko::Blob::new(Arc::new(self.data)), self.index)
+    }
+}
+
 impl Convert<kurbo::Join> for LineJoinStyle {
     fn convert(self) -> kurbo::Join {
         match self {