`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.
This PR fixes a numbe of interconnected bugs:
* We weren't consistently uploading a dirty BitmapData to the render
backend before drawing to/from it.
* BitmapData.draw should *not* add a fill color - it should draw over
the current contents of the BitmapData
* After drawing to a non-transparent BitmapData, we need to manually
set the opacity back to 255 for each pixel (the drawing process
takes transparency into account, but the opacity information is
thrown away at the end).
Nathan Adams