There are no longer any importers of package backend outside of
gioui.org/gpu. Move it internally, and rename it to the slightly more
specific "driver" while we're at it.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
The convert program is only used by the shaders from package gpu, and
we're about to make the backend package imported by the program internal
to package gpu. Move the converter below package gpu.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Elias Naur