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/vello_backend.rs

@@ -402,13 +402,11 @@ impl GenericDrawTarget for VelloDrawTarget {
                 SHARED_FONT_CACHE.with(|font_cache| {
                     let identifier = template.identifier();
                     if !font_cache.borrow().contains_key(&identifier) {
-                        font_cache.borrow_mut().insert(
-                            identifier.clone(),
-                            peniko::Font::new(
-                                peniko::Blob::from(run.font.data().as_ref().to_vec()),
-                                identifier.index(),
-                            ),
-                        );
+                        let Ok(font) = run.font.font_data_and_index() else {
+                            return;
+                        };
+                        let font = font.clone().convert();
+                        font_cache.borrow_mut().insert(identifier.clone(), font);
                     }
 
                     let font_cache = font_cache.borrow();