When preprocessing only, some tokens were emitted as <bad token>.
This fixes them to preserve their original content.

This supplants PR #182, with a correction and test results.

HLSL: Add GatherRed/Green/Blue/Alpha methods, inc 4-offset forms

HLSL: allow semicolons between global scope declarations

From the ES spec + Bugzilla 15931 and GL_KHR_vulkan_glsl:
- Update precision qualifiers for all built-in function prototypes.
- Implement the new algorithm used to distinguish built-in function
  operation precisions from result precisions.
Also add tracking of separate result and operation precisions, and
use that in generating SPIR-V.
(SPIR-V cares about precision of operation, while the front-end
cares about precision of result, for propagation.)

HLSL: Fixing some casts that warn when compiled to 64 bit (size_t is 64 bit…

The sequence

  #define m()
  int m"

creates a token of no length (a string of 0 size).  Protect
against a string of 0 size as well as the existing protect
against a null string.

This would look ahead for a second #, for token pasting, and if not
found, backup one token.  This is fine, unless at the end of line,
which would backup the #, rather than the look ahead.

HLSL: allow trailing commas in initializer lists & scalar initialization

HLSL: Fix a grammar error related to constructors in paren expr

Single member structs initialized with an initializer list had
an incorrect argument for constructor emulation.

SPV: Fix an issue of ++/-- for dvec/dmat.

Also, this allows turning on the error check for a failed assigment
when parsing.

This makes 39 HLSL tests have a working assignment that was previously
silently dropped, due to lack of this functionality.

HLSL: add Buffer support for Load method

HLSL: add missing vec,vec,scalar form of lerp(), + test

HLSL: allow uint literals, and add test for numeric suffixes

HLSL: Add CalculateLevelOfDetail, and unimplemented errors for *Uncla…

Missing are implicit conversions between int/bool/etc.

Starting out with this turned off, so tests can be locally fixed,
then will turn it on.

HLSL: add 2DMS texture formats, and matching Load / GetDimensions sup…

Apply the interpolation first, then apply the swizzle to the result,
the inverse of the order requested by the AST.  This fixes issue #411.