These introduce limited support for 8/16-bit types such that they can only be accessed in buffer memory and converted to/from 32-bit types.

Contributed from Khronos-internal work.

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

- Support new opaque types: f16sampler*, f16image*, f16subpassInput*.
- Add new built-in GLSL texture/image functions.

Constants were generally cached by type opcode, but all structures share the
same type opcode (OpTypeStruct), so they need to be cached by type id.

See https://github.com/KhronosGroup/GLSL/pull/11.

- correct inheritence (or not) of the right XFB buffer
- compute implicit stride (fixes #1212)
- semantic check block-member redeclarations
- inherit stride from a member

The memory model group agreed to these definitions for how
to map GLSL barrier, memoryBarrier, etc. With HLSL following suit.

Also, only emit this XFB information where the SPIR-V spec says
it should be emitted: essentially, on objects.

This and the previous commit together fix #1185.

This implementation uses the GLSL extension
GL_NV_conservative_raster_underestimation to generate the new SPIR-V
FullyCoveredEXT built in.

Fixes #1158.
Fixes #1159.

Desktop defaults to highp for samplers, but this should not apply to the built-in
functions, so make it appy only to user declarations.

Add support for Subpass Input proposal of issue #1069.

Subpass input types are given as:

    layout(input_attachment_index = 1) SubpassInput<float4> subpass_f;
    layout(input_attachment_index = 2) SubpassInput<int4>   subpass_i;
    layout(input_attachment_index = 3) SubpassInput<uint4>  subpass_u;

    layout(input_attachment_index = 1) SubpassInputMS<float4> subpass_ms_f;
    layout(input_attachment_index = 2) SubpassInputMS<int4>   subpass_ms_i;
    layout(input_attachment_index = 3) SubpassInputMS<uint4>  subpass_ms_u;

The input attachment may also be specified using attribute syntax:

    [[vk::input_attachment_index(7)]] SubpassInput subpass_2;

The template type may be a shorter-than-vec4 vector, but currently user
structs are not supported.  (An unimplemented error will be issued).

The load operations are methods on objects of the above type:

    float4 result = subpass_f.SubpassLoad();
    int4   result = subpass_i.SubpassLoad();
    uint4  result = subpass_u.SubpassLoad();

    float4 result = subpass_ms_f.SubpassLoad(samp);
    int4   result = subpass_ms_i.SubpassLoad(samp);
    uint4  result = subpass_ms_u.SubpassLoad(samp);

Additionally, the AST printer could not print EOpSubpass* nodes.  Now it can.

Fixes #1069

Added support for both extension GL_ARB_post_depth_coverage and GL_EXT_post_depth_coverage.

They are almost identical to the already supported GL_EXT_multiview

- Add int16 types (int16_t, uint16_t, i16vec, u16vec).
- Add int16 support to GLSL operators.
- Add int16 type conversions (to int16, from int16).
- Add int16 built-in functions.

Because it is valid in HLSL to alias bindings:
A) remove validation that aliasing is not done
B) make the algorithms tolerate aliasing

Adds a transformation step to the post processing step.
Two modes are available:
1) keep
- Keeps samplers, textures and sampled textures as is
2) transform pure texture into sampled texture and remove pure samplers
- removes all pure samplers
- transforms all pure textures into its sampled counter part

Change-Id: If54972e8052961db66c23f4b7e719d363cf6edbd

Fixes Vulkan Khronos-internal issue 770.

Longer term, this storage class should be generated based on the mode
of compilation.

These correspond to SPV_KHR_device_group and SPV_KHR_multiview.
Also, bring tests up to date with Khronos internals, and some misc. related changes.