Add support for EGL_EXT_gl_colorspace_bt2020_hlg to libEGL

This implements EGL_EXT_gl_colorspace_bt2020_hlg in terms of HAL
data formats such that applications can create HLG encoded surfaces. As
per the spec, applications need to ensure correct HLG encoding, which
made it possible to implement this extension without involving the
driver.

The change includes a manual update of eglext.h because the spec
is not yet ready.
https://github.com/KhronosGroup/EGL-Registry/pull/177

Test: Manually ran tests implemented in dEQP in a separate change
https://gerrit.khronos.org/c/vk-gl-cts/+/11608

Bug: 277210442

Change-Id: I3e011a786930d978fbc0d86aad29d25e4cdcc148