[NVPTX][AsmPrinter] Demonstrate usage of NVPTXTargetAsmStreamer in NVPTXAsmPrinter. (#188539)
Currently NVPTXAsmPrinter uses intermediate strings to generate ASM and
emit directly to output streamer as raw text. This PR demonstrates how
the printer can be updated to use NVPTXTargetAsmStreamer instead,
thereby getting rid of the intermediate strings. This is shown only for
the PTX header and module level directives.