And relax naming requirements of input and output files.

* Physical storage buffer cannot be used with OpConstantNull,
OpPtrEqual, OpPtrNotEqual or OpPtrDiff
  * new tests
  * see also #2929

* reduce: add -o. 
* reduce: add --temp-file-prefix. 
* reduce: add interestingness test args. 
* Detect bad args with one dash e.g. -a. 
* reduce: fix validator args. 
* Add = to args that require it. 
* More consistent naming/style across fuzz/reduce. 
* Change some 0 exit codes to 1.

)

Adds a spirv-fuzz option for converting a SPIR-V shader into a shader
that renders red, whilst containing the body of the original shader.
This is for aiding in compiler crash bug reporting.

Fixes #2929.

We want to handle OpKill better.  The wrap opkill causes lots of extra
code to be generated, even when they are not needed to avoid the main
problem: OpKill cannot be found directly in a continue construct.

This change will be more selective on which functions the OpKill will be
wrapped and inlining will avoid inlining.

Fixes #2912

A new pass that allows the fuzzer to change the 'selection control'
operand of OpSelectionControl instructions.

Fixes #2937.

Issue #2919 identifies a problem in spirv-fuzz's ability to determine
when it is safe to add a new control flow edge without breaking
dominance rules.  This change adds a (currently disabled) test to
expose the issue, and a comment to document that the current solution
is incomplete.

* Remove Impl struct in Reducer; we can re-add it later (in a cleaner fashion) if we need to. 
* Add cleanup passes in Reducer; needed so that removal of constants can be disabled during the main passes, and then enabled during cleanup passes, otherwise some main passes can perform worse due to lack of available constants. 
* Delete passes: remove op name, remove relaxed precision. And delete associated tests. 
* Add more tests for remove unreferenced instructions. 
* Always return and write the output file, even if there was a reduction failure. 
* Only exit with 0 if the reduction completed or we hit the reduction step limit.

Adds a fuzzer pass and transformation to create a composite (array,
matrix, struct or vector) from available constituent components, and
inform the fact manager that each component of the new composite is
synonymous with the id that was used to construct it. This allows the
"replace id with synonym" pass to then replace uses of said ids with
uses of elements extracted from the composite.

Fixes #2858.

Fixes #2889