This reverts commit 1dd65ca3, reversing
changes made to 4960baaf.

HLSL: support per control point patch const fn invocation

HLSL: Fix #804: crash on empty sequence node passed to intrinsic expansions

The SPIR-V generator had assumed tessellation modes such as
primitive type and vertex order would only appear in tess eval
(domain) shaders.  SPIR-V allows either, and HLSL allows and
possibly requires them to be in the hull shader.

This change:

1. Passes them through for either tessellation stage, and,

2. Does not set up defaults in the domain stage for HLSl compilation,
to avoid conflicting definitions.

HLSL: allow length() on scalars

Covers if(cond), while(cond), do-while(cond), for(;cond;), and (cond ? :).
Fixes #778.

Unknown how extensive the semantics need to be yet. Need real
feedback from workloads. This is just done as part of unifying it
with the class/struct namespaces and grammar productions.

HLSL HS outputs a per ctrl point value, and the DS reads an array
of that type.  (It also has a per patch frequency).  The per-ctrl-pt
frequency is arrayed on just one side, as opposed to SPIR-V which
is arrayed on both.  To match semantics, the compiler creates an
array behind the scenes and indexes it by invocation ID, assigning
the HS return value to it.

SPIR-V requires that tessellation factor arrays be size 4 (outer) or 2 (inner).
HLSL allows other sizes such as 3, or even scalars.  This commit converts
between them by forcing the IO types to be the SPIR-V size, and allowing
copies between the internal and IO types to handle these cases.

This PR emulates per control point inputs to patch constant functions.
Without either an extension to look across SIMD lanes or a dedicated
stage, the emulation must use separate invocations of the wrapped
entry point to obtain the per control point values.  This is provided
since shaders are wanting this functionality now, but such an extension
is not yet available.

Entry point arguments qualified as an invocation ID are replaced by the
current control point number when calling the wrapped entry point.  There
is no particular optimization for the case of the entry point not having
such an input but the PCF still accepting ctrl pt frequency data.  It'll
work, but anyway makes no so much sense.

The wrapped entry point must return the per control point data by value.
At this time it is not supported as an output parameter.

HLSL: Fix an issue of frexp().

Don't emit NV-specific interface members if NV extensions are disabled.

The "exp" parameter is floating-point type in HLSL intrinsic while it is
integer type in GLSL built-in function.

HLSL: fix crash on empty struct return from entry point

This allows global initializers to use $Global members.

Thanks to @steve-lunarg for his input and discussions on handling member functions.

Another precurser to getting member non-static functions working.

HLSL: use prefix for builtin functions names to avoid namespace colli…

HLSL: Buffer types should be unsampled.

It would have been possible for globally scoped user functions to collide
with builtin method names.  This adds a prefix to avoid polluting the
namespace.

Ideally this would be an invalid character to use in user identifiers, but
as that requires changing the scanner, for the moment it's an unlikely yet
valid prefix.

Still need: pass by reference in SPIR-V and symbol-table level
for accessing 'this' members from member functions.

Also use this to move deferred member-function-body parsing to a better
place.

This should also be well poised for implementing the 'namespace' keyword.

RWBuffer objects were generating (properly) unsampled resoures, while
Buffer objects were not.  This fixes that.