linker: Add tests for various type comparisons (#2613)

This adds a number of tests that check that all types will match to
identically written clones during linking, including nearly every Type
and some combinations (e.g. Functions of Arrays of Floats). Intent is
for use with https://github.com/KhronosGroup/SPIRV-Tools/pull/2580,
however that PR focuses on issues with TypeArray whereas these tests are
(more) comprehensive and test more subtle (and possibly incorrect)
cases.

A number of these tests fail, many are fixed by the aforementioned PR.
Some additional tests involving TypeForwardPointer are currently
disabled as they cause assertion failures.