HLSL: allow implicit array sizing.

In HLSL array sizes need not be provided explicitly in all circumstances.
For example, this is valid (note no number between the [ ]):

  // no explicit array size
  uniform float g_array[] = { 1, 2, 3, 4, 5 };

This PR does not attempt to validate most invalid cases.

A new test is added to verify the resulting linker objects.