Use IRBuilder to refactor llpcPatchCopyShader
Use IRBuilder to refactor llpcPatchCopyShader

- Use IRBuilder to rewrite codes constructing IR. This will simplify the
  statements and make codes more readable.
- Inline args to EmitCall if necessary. This will make args close to
  EmitCall and is easy to check what args are.
- Remove "llvm" prefix since this is a source file and "using namespace
  llvm" is specified.
- Rename LoadValueFromGsVsRingBuffer to LoadValueFromGsVsRing. For on-chip
  GS, the ring is on LDS, not on buffer. This makes it more general.

googlestadia/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc,googlestadia/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc