Add support for floating point configs. On backends that
support rendering to floating point formats, add them to
EGL's frambuffer config list

Bug: angleproject:3958
Tests: dEQP-EGL.functional.wide_color.*fp16*
       angle_end2end_tests --gtest_filter=EGLFloatSurfaceTest*
Change-Id: Ie65f63013483267985c2b308567bf5025acf750e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1993686
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>