Don't use BGRA8 unless GL_EXT_texture_storage is available
Don't use BGRA8 unless GL_EXT_texture_storage is available

We recently changed to use the glTexStorage* family of functions,
along with sized internal format types, such as BGRA8. Unfortunately,
the GL_EXT_texture_format_BGRA8888 extension does not provide BGRA8 as
a valid format unless the GL_EXT_texture_storage extension is also
available, which is not usually the case on GLES3 as glTexStorage*
are built in.

Unfortunately this means we must fall back to using glTexImage* rather
than glTexStorage* when dealing with BGRA data. Longer term it will
make sense to ensure the provided data is in RGBA format, as the
benifits of immutable storage are desirable.

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