arb_gpu_shader_int64: Test int64-related shift operators more thoroughly
Adds tests trying 64-bit scalars on RHS, and 32&64 integer vectors on both sides. Could've caught mesa#6862 (closed) and caught a related bug.
Fixes: 7a11be33 ("arb_gpu_shader_int64: add test generation to standard testing template")
Signed-off-by: Sviatoslav Peleshko sviatoslav.peleshko@globallogic.com