gl.xml: Add GL_FRAMEBUFFER_SRGB_EXT to EnableCap group. Add GL_EXT_sRGB_write_control in registry_xml.py. This makes FrameCapture write a GL_FRAMEBUFFER_SRGB_EXT enum instead of it's hex value in glEnable/Disable calls. Bug: angleproject:5857 Change-Id: Ifa01118c2958275c7623c6bfe29f015fa8875fce Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2988356 Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Lubosz Sarnecki <lubosz.sarnecki@collabora.com>