Add mode to allow unbounded layout(set = N) values

[HansKristian-Work]

With EXT_descriptor_heap, set decoration is completely virtual and can take any value. However, when compiling this shader

#version 450

layout(set = 300, binding = 400) uniform sampler2D blah;
layout(location = 0) out vec4 FragColor;

void main()
{
        FragColor = texture(blah, vec2(0.5));
}

/tmp/test.frag
ERROR: /tmp/test.frag:3: 'set' : set is too large 
ERROR: /tmp/test.frag:3: '' : compilation terminated 
ERROR: 2 compilation errors.  No code generated.


ERROR: Linking fragment stage: Missing entry point: Each stage requires one entry point

It would be good to have some way to bypass this limit from the CLI and API. This is causing problems in vkd3d-proton since we use rather large set values to parcel out the set space to tables vs root desc vs root constant, etc.

[arcady-lunarg]

Right now it is also a glslang implementation limitation since the layoutSet field in TQualifier is a bitfield that allows a maximum value of 0x3f, which was enough for what Vulkan implementations supported with the traditional binding model. Would it be sufficient to lift this limitation only when the descriptor heap extension is enabled, or is some kind of command line flag the better option here?