Nightly 2022-11-23

render: Don't use BitmapHandle in tessellator

Currently, we rely on ShapeTessellator being able to get a BitmapHandle
without a RenderBackend. With the upcoming BitmapData refactor,
we will always need a RenderBackend to get a BitmapHandle, which creates
borrow-checker issues in ShapeTessellator (which is stored in a
RenderBackend).

To solve this, we split BitmapSource.bitmap into two methods -
BitmapSource.bitmap and BitmapSource.bitmap_handle. ShapeTessellator
continues to use BitmapSource.bitmap, and uses the u16 bitmap id
instead of a BitmapHandle. The BitmapSource.bitmap_handle method
is used inside each render backend to convert the id to a BitmapHandle,
avoiding borrow-checker issues.