fuzz: add shrinker-temp-file-prefix (#2928)
fuzz: add shrinker-temp-file-prefix (#2928)

And relax naming requirements of input and output files.
antiagainst/SPIRV-Tools,dneto0/SPIRV-Tools,pierremoreau/SPIRV-Tools,pierremoreau/SPIRV-Tools,pierremoreau/SPIRV-Tools,KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools,antiagainst/SPIRV-Tools,dneto0/SPIRV-Tools,pierremoreau/SPIRV-Tools,dneto0/SPIRV-Tools,KhronosGroup/SPIRV-Tools,pierremoreau/SPIRV-Tools,dneto0/SPIRV-Tools,pierremoreau/SPIRV-Tools,pierremoreau/SPIRV-Tools,KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools,dneto0/SPIRV-Tools,antiagainst/SPIRV-Tools,antiagainst/SPIRV-Tools,KhronosGroup/SPIRV-Tools,dneto0/SPIRV-Tools,dneto0/SPIRV-Tools,antiagainst/SPIRV-Tools,KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools,dneto0/SPIRV-Tools,pierremoreau/SPIRV-Tools