Add support for creating 2D array EGLImages. 2D array
textures are core in GLES3.0. Enable the eglImageArray
bool that controls exposure of the extension for all
contexts >= GLES3.0

Bug: angleproject:4604
Tests: angle_end2end_tests --gtest_filter=ImageTest.*2DArray*
Change-Id: Iebc1ad184fe7209ca89d620290337438ac251c56
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2176109
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>