In OpenGL, GL_INT is expected for sampler uniforms. Before this
our emitted code was using the underlying return type, which can be
unsigned, leading to glUniformuiv.

Also, don't try to set image uniforms with glUniform calls, it is
not allowed.

Test: Fortnite MEC
Bug: b/170755560
Change-Id: I6786df487285fee77cfe792dfa85eb17feb155e9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2611557
Commit-Queue: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>