Adding validation for OpSpecConstantComposite.

Adding validation for OpSpecConstantComposite.

SpecConstantComposite may specialize to a vector, matrix, array, or
struct. In each case, the number of components and type of components
that are being specialized to must match the expected result type.

Removed use of macros in these tests.
Now using the spvValidateBase class. Using CompileSuccessfully(), and
ValidateInstructions() to compile to binary and run the validator. Also
using getDiagnosticString() to check the proper error message string.
All the heavy lifting is done in ValidateBase class.