Put TestFixture.h classes in a namespace. Remove unused #includes.
Since now we can distinguish between def and use according to the variable's location, there is no need to keep two variable prefixes. Also reformat tests to use the value generating instruction format ("<result-id> = <opcode> <operand>..").
This commit contains the source for the SPIRV static library, spirv-as, spirv-dis, and spirv-val tools.