* Bump bitflags to 2.0.0
* Sprinkle Clone, Copy, Eq, PartialEq, and Debug derives where needed
* Call `bits` on bitflags, as it is now a method
* Switch from `from_bits_truncate` to `from_bits_retain` on bitflags where needed
* Bump h263-rs for the bitflags 2.0.0 dependency
As part of porting to bitflags 2.0.0, see:
https://kodraus.github.io/rust/2022/10/07/bitflags2.html#upgrading-to-2x
`BitmapHandle` now holds `Arc<dyn BitmapHandleImpl>`.
This allows us to move all of the per-bitmap backend data into
`BitmapHandle`, instead of holding an id to a backend-specific
hashmap.
This fixes the memory leak issue with bitmaps. Once the AVM side of a
bitmap (`Bitmap`/`BitmapData`) gets garbage-collected, the
`BitmapHandle` will get dropped, freeing all of the GPU resources
assoicated with the bitmap.
We only called `get_bitmap_pixels` when creating a `BitmapData`
for an SWF-provided `Bitmap`. We now store the initial pixels
in `Character::Bitmap`, and use them to initialize a `BitmapData`
when needed.
This lets us simplify the wgpu backend, which no longer needs
to store a `Bitmap` object. In addition to saving space for
`BitmapData` objects that lack an SWF `Bitmap`, this will make
it easier to move data from `bitmap_registry` into `BitmapHandle`
itself.