GL: Fix glClearTexImage for LUMA textures We need to transform the format and type before handing it off to the driver for emulated texture formats. Bug: angleproject:347047859 Change-Id: Ifa2c92179a49fbd8ae152a365c2915091102e4e6 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5645626 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>