Merge branch '25-spirv-special-instruction-tests' into 'master'

25 SPIR-V assembly tests based on compute shader

- OpConstantNull
- OpConstantComposite
- OpLine
- OpNoLine
- OpSource
- OpSourceContinued
- OpUndef
- OpUnreachable
- Loop control
- Selection control
- Function control
- Block order
- OpSourceExtension
- OpPhi
- decoration group

Also change input to random numbers for the OpNop test.

See merge request !44