Add support for embedding resources in the rust generator

This is relatively straight-forward via a pass in the compiler to
collect the resources to embed and then use include_bytes! (once per
resource).

What's really annoying is that the rust resource enum can't store a
&'static [u8] because cbindgen doesn't represent that, probably because
the slice representation isn't guaranteed to stay as it is. So instead
this, for now, uses raw pointers.

sixtyfps_runtime/corelib/abi/datastructures.rs

@@ -208,12 +208,19 @@ impl Color {
 /// system or embedded in the resulting binary. Or they might be URLs to a web server and a downloaded
 /// is necessary before they can be used.
 #[derive(Clone, PartialEq, Debug)]
-#[repr(C)]
+#[repr(u8)]
 pub enum Resource {
     /// A resource that does not represent any data.
     None,
     /// A resource that points to a file in the file system
     AbsoluteFilePath(crate::SharedString),
+    /// A resource that is embedded in the program and accessible via pointer
+    EmbeddedData {
+        /// raw pointer to the read-only data
+        ptr: *const u8,
+        /// size of the embedded data
+        len: usize,
+    },
 }
 
 impl Default for Resource {