This prevents potentional sharing from inadvertently affecting other arrays.

This will help in expanding flattening and reducing splitting.

HLSL: implement #pragma pack_matrix(layout)

This adds support for #pragma pack_matrix() to the HLSL front end.

The pragma sets the default matrix layout for subsequent unqualified matrices
in structs or buffers. Explicit qualification overrides the pragma value. Matrix
layout is not permitted at the structure level in HLSL, so only leaves which are
matrix types can be so qualified.

Note that due to the semantic (not layout) difference in first matrix indirections
between HLSL and SPIR-V, the sense of row and column major are flipped.  That's
independent of this PR: just a factor to note.  A column_major qualifier appears
as a RowMajor member decoration in SPIR-V modules, and vice versa.

Includes related trackLinkage() code removal and name improvements.

HLSL: fix qualifier propagation from user struct types to block defin…

The HLSL FE tracks four versions of a declared type to avoid losing information, since it
is not (at type-decl time) known how the type will be used downstream.  If such a type
was used in a cbuffer declaration, the cbuffer type's members should have been using
the uniform form of the original user structure type, but were not.

This would manifest as matrix qualifiers (and other things, such as pack offsets) on user struct
members going missing in the SPIR-V module if the struct type was a member of a cbuffer, like so:

    struct MyBuffer
    {
        row_major float4x4 mat1;
        column_major float4x4 mat2;
    };

    cbuffer Example
    {
        MyBuffer g_MyBuffer;
    };

Fixes: #789

This allows removal of isPerVertexBuiltIn(). It also leads to
removal of addInterstageIoToLinkage(), which is no longer needed.

Includes related name improvements.

The goal is to flatten all I/O, but there are multiple categories and
steps to complete, likely including a final unification of splitting
and flattening.

GLSL: Add GLSL 4.60 features

Most of this was obsoleted by entry-point wrapping.
Some other is just unnecessary.
Also, includes some spelling/name improvements.

This is to help lay ground work for flattening user I/O.

HLSL: Non-functional: warning fix + remove unused member

Two non-functional changes:

1. Remove flattenLevel, which is unneeded since at or around d1be7545.

2. Fix build warining about unused variable in executeInitializer.

SPV: Memory qualifiers should decorate top-level block members

HLSL: handle multiple clip/cull semantic IDs

HLSL allows several variables to be declared.  There are packing rules involved:
e.g, a float3 and a float1 can be packed into a single array[4], while for a
float3 and another float3, the second one will skip the third array entry to
avoid straddling

This is implements that ability.  Because there can be multiple variables involved,
and the final output array will often be a different type altogether (to fuse
the values into a single destination), a new variable is synthesized, unlike the prior
clip/cull support which used the declared variable.  The new variable name is
taken from one of the declared ones, so the old tests are unchanged.

Several new tests are added to test various packing scenarios.

Only two semantic IDs are supported: 0, and 1, per HLSL rules.  This is
encapsulated in

     static const int maxClipCullRegs = 2;

and the algorithm (probably :) ) generalizes to larger values, although there
are a few issues around how HLSL would pack (e.g, would 4 scalars be packed into
a single HLSL float4 out reg?  Probably, and this algorithm assumes so).

Fix dref explicit LOD form of sample with cube texture arrays

The dref parameter was being used as the LOD.  Now it it's properly the dref.

HLSL: Fix crash with --resource-set-binding [n] (global form, not per-register form)