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/shared/fonts/Cargo.toml

@@ -12,6 +12,7 @@ name = "fonts_traits"
 path = "lib.rs"
 
 [dependencies]
+ipc-channel = { workspace = true }
 malloc_size_of = { workspace = true }
 malloc_size_of_derive = { workspace = true }
 range = { path = "../../range" }

components/shared/fonts/lib.rs

@@ -6,6 +6,7 @@
 
 use std::sync::Arc;
 
+use ipc_channel::ipc::IpcSharedMemory;
 use malloc_size_of_derive::MallocSizeOf;
 use range::{RangeIndex, int_range_index};
 use serde::{Deserialize, Serialize};
@@ -18,3 +19,42 @@ int_range_index! {
 }
 
 pub type StylesheetWebFontLoadFinishedCallback = Arc<dyn Fn(bool) + Send + Sync + 'static>;
+
+/// A data structure to store data for fonts. Data is stored internally in an
+/// [`IpcSharedMemory`] handle, so that it can be sent without serialization
+/// across IPC channels.
+#[derive(Clone, MallocSizeOf)]
+pub struct FontData(#[conditional_malloc_size_of] pub(crate) Arc<IpcSharedMemory>);
+
+impl FontData {
+    pub fn from_bytes(bytes: &[u8]) -> Self {
+        Self(Arc::new(IpcSharedMemory::from_bytes(bytes)))
+    }
+
+    pub fn as_ipc_shared_memory(&self) -> Arc<IpcSharedMemory> {
+        self.0.clone()
+    }
+}
+
+impl AsRef<[u8]> for FontData {
+    fn as_ref(&self) -> &[u8] {
+        &self.0
+    }
+}
+
+/// Raw font data and an index
+///
+/// If the font data is of a TTC (TrueType collection) file, then the index of a specific font within
+/// the collection. If the font data is for is single font then the index will always be 0.
+#[derive(Clone)]
+pub struct FontDataAndIndex {
+    /// The raw font file data (.ttf, .otf, .ttc, etc)
+    pub data: FontData,
+    /// The index of the font within the file (0 if the file is not a ttc)
+    pub index: u32,
+}
+
+#[derive(Copy, Clone, PartialEq)]
+pub enum FontDataError {
+    FailedToLoad,
+}