Previously, casting an object of a struct type to an identical type
would produce an error.  This PR allows this case.

As a side-effect of the change, several self-type casts in existing
tests go away.  For example:

    0:10          Construct float ( temp float)
    0:10            'f' ( in float)

becomes this (without the unneeded constructor op):

    0:10          'f' ( in float)

For vector or array types this can result in somewhat less overall code.

Fixes: #1218

SPIR-V requires the coverage mask to be an array of integers, but HLSL
allows scalar integers.  This adds the requisite type conversion and
wrapped entry point handling.

Fixes: #1202

This PR forces the external definition of SV_GroupID variables to 3-vectors.
The conversion process between the shader-declared type and the external type
happens in wrapped main IO variable conversion.

The same applies to SV_DispatchThreadID and SV_GroupThreadID.

Fixes: #1371

Append() method is special: unlike most outputs, it does not copy
some temporary data to a symbol in the entry point epilogue, but
rather uses an emit builtin after each write to the output stream.

This had been handled by remembering the special output symbol for
the stream as it was declared in the shader entry point before
symbol sanitization.  However the prior code was too simple and
only handled cases where the Append() method happened after the
entry point, so that the output symbol had been seen.

This PR adds a patching step so that the Append()s may appear in
any order WRT the entry point.  They are patched in an epilogue,
whereupon it is guaranteed in a well formed shader that we have
seen the appropriate declaration.

Fixes #1217.

We want these tests to be independent of whether SPIRV-opt is used.

Initial way of addressing #1362.

It was missing when there were no semantics.

- Use much simpler method to update implicit array sizes.
  The previous overly complicated method was error prone.
- Rationalize all use of unsized arrays.
- Combine decorations when generating SPIR-V, to simplify
  adding extensions.

Also update spirv-opt recipes.

There a couple functional problems, which when reduced down also led to
some good simplifications and rationalization.  So, this commit:
 - corrects "mixed" functionality: int[A] f[B] -> f[B][A]
 - correct multi-identifier decls: int[A] f[B], g[C] -> f and g are independently sized.
 - increases symmetry between different places in the code that do this
 - makes fewer ways to do the same thing; several methods are just gone now
 - makes more clear when something is copied or shared

This effects 60 tests, in a trivial way, but is critical to factor out this
noise from future planned changes.

Fixes #1295.

Tokens that are accepted by any version of HLSL or GLSL should be
allowed when #ifdef'd off, such that errors are not reported.

Enabled via -fhlsl_functionality1

The base and shift amount need to be integers, but not of the same type.
This fixes #1296 and replaces #1297.

Reinforces that conversion rules are operation-specific.
Side effect is that HLSL logical-operator conversions are more direct
(e.g. float -> bool, rather than float -> int -> bool).