Complete the implementation of GL_EXT_buffer_storage Currently, glBufferStorageEXT doesn't set buffer usage to DYNAMIC_DRAW. Also, validation of glGetBufferParameter* misses check for GL_BUFFER_IMMUTABLE_STORAGE_EXT and GL_BUFFER_STORAGE_FLAGS_EXT. This patch fixes these issues. Also, an end2end test is added. Bug: angleproject:399689628 Change-Id: Iecf6bd921f4fff849a5f059adf40043d08edfb7a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6312515 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com>