Addition of the entry points for
EXT_shader_framebuffer_fetch_non_coherent extension.

Bug: angleproject:5454
Change-Id: I2b8ba5141eed61a0c3ba58aeb2eec12a2071e7f1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2590991
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>