Per spec, in eglCreateContext when client version attributes are invalid - set
EGL_BAD_ATTRIBUTE. Set EGL_BAD_MATCH when config is not compatible.
Rename config variables in ValidateCompatibleConfigs to distinguish context
from surface configs. Context config handled differently when EGL_NO_CONFIG.

Bug: angleproject:3755
Test: angle_end2end_tests --gtest_filter=EGLCreateContextAttribsTest*
Change-Id: Iaea57653cf643ff60c8d4eabd3f022306bf1f4ca
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1747298Reviewed-by: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>