Add comments and format `gtGetThisArg`.
Add comments and format `gtGetThisArg`.

krk/coreclr,poizan42/coreclr,wtgodbe/coreclr,krk/coreclr,krk/coreclr,poizan42/coreclr,cshung/coreclr,cshung/coreclr,wtgodbe/coreclr,wtgodbe/coreclr,poizan42/coreclr,krk/coreclr,wtgodbe/coreclr,cshung/coreclr,cshung/coreclr,cshung/coreclr,wtgodbe/coreclr,wtgodbe/coreclr,poizan42/coreclr,krk/coreclr,poizan42/coreclr,cshung/coreclr,poizan42/coreclr,krk/coreclr