Refactor in preparation of adding OES_depth_texture Rename existing depthTexture extension flag to depthTextureANGLE to distinguish it from OES depth texture extension to be added. Bug: angleproject:3103 Test: angle_end2end_tests --gtest_filter=DepthStencilFormatsTest.DepthTexture Change-Id: I44c69a69b925a84f931518e0374e662893813061 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1575425 Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>