Add Find-Dotnet to make build module smarter
Add Find-Dotnet to make build module smarter

New function smartly adds the probable location of the .NET CLI tools to
the path if `dotnet` is not found. If it is still not found, it restores
the path. All functions using `dotnet` should call `Find-Dotnet` first.

KarolKaczmarek/PowerShell,daxian-dbw/PowerShell,KarolKaczmarek/PowerShell,TravisEz13/PowerShell,jsoref/PowerShell,kmosher/PowerShell,jsoref/PowerShell,KarolKaczmarek/PowerShell,TravisEz13/PowerShell,jsoref/PowerShell,KarolKaczmarek/PowerShell,bmanikm/PowerShell,bingbing8/PowerShell,JamesWTruher/PowerShell-1,jsoref/PowerShell,kmosher/PowerShell,JamesWTruher/PowerShell-1,bmanikm/PowerShell,daxian-dbw/PowerShell,daxian-dbw/PowerShell,kmosher/PowerShell,bingbing8/PowerShell,PaulHigin/PowerShell,TravisEz13/PowerShell,bingbing8/PowerShell,PaulHigin/PowerShell,jsoref/PowerShell,PaulHigin/PowerShell,JamesWTruher/PowerShell-1,TravisEz13/PowerShell,bmanikm/PowerShell,KarolKaczmarek/PowerShell,kmosher/PowerShell,bingbing8/PowerShell,bmanikm/PowerShell,PaulHigin/PowerShell,kmosher/PowerShell,JamesWTruher/PowerShell-1,bingbing8/PowerShell,daxian-dbw/PowerShell,bmanikm/PowerShell