This PR sets the TQualifier layoutFormat according to the HLSL image type.
For instance:

  RWTexture1D <float2> g_tTex1df2;

becomes ElfRg32f.  Similar on Buffers, e.g, Buffer<float4> mybuffer;

The return type for image and buffer loads is now taken from the storage format.
Also, the qualifier for the return type is now (properly) a temp, not a global.

HLSL: phase 2: add operator[]

Check for out-of-range bindings during IO mapping.

- hlsl.struct.frag variable changed to static, assignment replacd.

- Created new low level functions addBinaryNode and addUnaryNode.  These are
  used by higher level functions such as addAssignment, and do not do any
  argument promotion or conversion of any sort.

- Two functions above are now used in RWTexture lvalue conversions.  Also,
  other direction creations of unary or binary nodes now use them, e.g, addIndex.
  This cleans up some existing code.

- removed handling of EOpVectorTimesScalar from promote()

- removed comment from ParseHelper.cpp

Improve comments.
A few tweaked lines allow [] on non-rw tx.  Add test case for this.
Improve VectorTimesScalar handling.

This commit splits lValueErrorCheck into machine dependent and independent
parts.  The GLSL form in TParseContext inherits from and invokes the
machine dependent part in TParseContextBase.  The base form checks language
independent things.  This split does not change the set of errors tested
for: the test results are identical.

The new base class interface is now used from the HLSL FE to test lvalues.
There was one test diff due to this, where the test was writing to a uniform.
It still does the same indirections, but does not attempt a uniform write.

This commit adds l-value support for RW texture and buffer objects.
Supported are:

- pre and post inc/decrement
- function out parameters
- op-assignments, such as *=, +-, etc.
- result values from op-assignments.  e.g, val=(MyRwTex[loc] *= 2);

Not supported are:
- Function inout parameters
- multiple post-inc/decrement operators.  E.g, MyRWTex[loc]++++;

This commit adds r-value support for RW textures and buffers.
Supported is:

- Function in parameter conversions
- conversion of rvalue use to imageLoad

SPV: Use SampledImage with OpImageQueryLod

Khronos SPIR-V issue #74

Address some compiler warnings.

SPV: Implement extension SPV_KHR_shader_draw_parameters.

Parser: Some function prototypes of interpolateAtXXX are incorrect.

- Add explicit casts from long to int.
- Comment out method argument names that are unused.
- Always initialize a boolean variable before it's read.

HLSL: phase 1: add RWTexture and RWBuffer

There's a lot to do for RWTexture and RWBuffer, so it will be broken up into
several PRs.  This is #1.

This adds RWTexture and RWBuffer support, with the following limitations:
  * Only 4 component formats supported
  * No operator[] yet

Those will be added in other PRs.

This PR supports declarations and the Load & GetDimensions methods.  New tests are
added.

Gtests can be run on another source tree

The gtest executable accepts a --test-root option to specify
a root directory for test files.  It defaults to the Test directory
in the source tree from which the executable is built.

For example, this lets us run test exectuables built with MinGW on Linux
on a Windows machine with its own copy of the source tree.

HLSL: fix for flattening assignments from non-symbol R-values.

If a member-wise assignment from a non-flattened struct to a flattened struct sees a complex R-value
(not a symbol), it now creates a temporary to hold that value, to avoid repeating the R-value.
This avoids, e.g, duplicating a whole function call.  Also, it avoids re-using the AST node, making a
new one for each member inside the member loop.

The latter (re-use of AST node) was also an issue in the GetDimensions intrinsic decomposition,
so this PR fixes that one too.

add reflection queries to return a TType.  Fix minor issue with inter…

- Add new queries: TProgram::getUniformTType and getUniformBlockTType,
  which return a const TType*, or nullptr on a bad index.  These are valid for
  any source language.

- Interface name for HLSL cbuffers is taken from the (only) available declaration name,
  whereas before it was always an empty string, which caused some troubles with reflection
  mapping them all to the same index slot.  This also makes it appear in the SPIR-V binary
  instead of an empty string.

- Print the binding as part of the reflection textual dump.

- TType::clone becomes const.  Needed to call it from a const method, and anyway it doesn't
  change the object it's called on.

- Because the TObjectReflection constructor is called with a TType *reference* (not pointer)
  so that it's guaranteed to pass in a type, and the "badReflection" value should use a nullptr
  there, that now has a dedicated static method to obtain the bad value.  It uses a private
  constructor, so external users can't create one with a nullptr type.

Non-functional: Rationalizing parse helper hierarchy, step 3 (effected editable symbols and IO resize).

Non-functional: Rationalizing parse helper hierarchy, step 2 (effected error messaging and cascading errors).

Change binding auto-map to use provided offsets.

Previously, the binding auto-mapping facility was free to use any unused
binding.  This change makes auto-bindings use the same offset value as
explicit bindings.