This is only the first step where we:
- clean-up some code to prepare for 2nd step
- add support for the linear->srgb in the shaders
The linear->srgb conversion is protected by a
specification constant and will be enabled only
if the corresponding EGL extension in not present.
Then, if enabled, the actual conversion is
controlled by a uniform so that it can be
selectively enabled on swapchains that have it
turned on.
In this change, the emulation logic that sets
these gates is not implemented (that's step 2).
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