This interface handles returning a bitmap given an ID and is used
by the render backend to get the bitmap used for a bitmap fill.
This will allow for bitmap fills in the drawing API, as these will
manage their own list of bitmaps.
This also removes the MovieLibrary dependency from render backends
and will allow for better decoupling in the future.
Matrices in an SWF file store their scale/skew components in
in 16.16 format (fbits).
Split `ruffle_core::Matrix` and `swf::Matrix`. `swf::Matrix` now
stores its data as `Fixed16` instead of immediately converting to
`f32`.
Pass the movie library to `register_shape` methods so that bitmap
charcter IDs can be resolved immediately on the proper SWF.
This fixes#2037, which cause incorrect bitmaps to be used when
multiple movies were loaded.
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