Cleaning up PixWinPlugin to use the correct header guards, correct types, and correct windows version check.
#jira none
#rb jeremy.moore
#preflight 61df36bea63213484e0a4e38
#ROBOMERGE-AUTHOR: christopher.waters
#ROBOMERGE-SOURCE: CL 18589786 in //UE5/Release-5.0/... via CL 18589808 via CL 18589826
#ROBOMERGE-BOT: STARSHIP (Release-Engine-Test -> Main) (v899-18417669)
[CL 18589846 by christopher waters in ue5-main branch]