Slang compiler version

See SlangVersion in frameworks/compile/slang/slang_version.h. The bitcode wrapper has a field that indicates the version of the slang compiler that produced that bitcode. A bitcode consumer is allowed to make certain assumptions if the version number is sufficiently high. However, only user bitcode has a wrapper -- libclcore.bc does not. Therefore, libclcore.bc must not violate ANY of the guarantees provided at a particular SlangVersion that allow the aforementioned assumptions. This is important because when user bitcode is linked to libclcore.bc (bcc::Script::LinkRuntime()) the linked bitcode is treated as having the same SlangVersion as the user bitcode. This implies that whenever we modify (runtime, driver, bcc) to take advantage of some new SlangVersion guarantee, we may have to update libclcore.bc to conform to that guarantee.