* opengl: remove unnecessery glflush calls
glflushing forces the driver to break batching and issue commands
prematurely and prevents optimisations like command reordering and
merging.
many glFunctions already internally glflushes and eglsync creation still
has a glflush at end render. so lets reduce the overhead of these calls.
* opengl: reduce glUseProgram calls
apitrace shows cases where the same program gets called multiple times,
add a helper function that keeps track of current program and only call
it once on same program. reduces slight overhead.
* opengl: use more efficient vertex array object
use a more modern vertex array object approach with the shaders, makes
it a onetime setup on shader creation instead of once per drawcall, also
should make the driver not have to revalidate the vertex format on each
call.
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