Fix EXT_texture_norm16 * Add norm16 format info for OpenGL backend * Add validation for newly introduced norm16 formats * Fix some logic of texture tests Bug: chromium:1000354, angleproject:1365 Change-Id: Ie6d6e5e276da4df4b7c667be28d324d4976b35ec Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1902720 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Shrek Shao <shrekshao@google.com> Commit-Queue: Shrek Shao <shrekshao@google.com>