Add validation for FramebufferTexture FramebufferTexture() was added as part of the geometry shader extension. However, it has become core in GLES 3.2. * Added validation for glFramebufferTexture(). * Added unit tests to check for validation errors for the OES and 3.2 core versions. Bug: angleproject:42262233 Change-Id: I2696d37bb54a26f0fe455107dca472cc05063fa6 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5605108 Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com>