arb_texture_view: Test NaN for some RGB32 clears
Before this patch, this test cleared a GL_RGB32F texture to a NaN (0xffffffff), then checked for that exact bit pattern from the texelFetch instruction. It's possible that HW may return a different NaN encoding, so update the clear program to check for NaN instead.
Enables iris to pass this test on gen11+.
Closes: #42 (closed)