Use string.Create in Path.GetRandomFilePath (dotnet/coreclr#21410)
Use string.Create in Path.GetRandomFilePath (dotnet/coreclr#21410)

* Use string.Create in Path.GetRandomFilePath

Removes a good chunk of the unsafe code.

* Address PR feedback

Signed-off-by: dotnet-bot <03c4cb6107ae99956a7681f2c97ff7104809a2bd@microsoft.com>

ViktorHofer/corefx,ericstj/corefx,ericstj/corefx,ericstj/corefx,ViktorHofer/corefx,shimingsg/corefx,ptoonen/corefx,shimingsg/corefx,ViktorHofer/corefx,wtgodbe/corefx,ptoonen/corefx,ViktorHofer/corefx,wtgodbe/corefx,wtgodbe/corefx,wtgodbe/corefx,wtgodbe/corefx,shimingsg/corefx,ptoonen/corefx,ViktorHofer/corefx,ViktorHofer/corefx,BrennanConroy/corefx,ericstj/corefx,ericstj/corefx,shimingsg/corefx,ptoonen/corefx,ptoonen/corefx,BrennanConroy/corefx,wtgodbe/corefx,shimingsg/corefx,ericstj/corefx,ptoonen/corefx,ericstj/corefx,BrennanConroy/corefx,shimingsg/corefx,ViktorHofer/corefx,wtgodbe/corefx,ptoonen/corefx,shimingsg/corefx