add SPIR-V 1.4 testing for Image Operands and Loop Controls

[bashbaug]

This PR adds targeted testing for SPIR-V 1.4 features. Specifically, this PR adds testing for:

1. The new Image Operand for SignExtend and ZeroExtend.
2. The new Loop Controls MinIterations, MaxIterations, IterationMultiple, PeelCount, and PartialCount.