Refactor .NET CLI installation into Install-Dotnet
Refactor .NET CLI installation into Install-Dotnet

So that it can be reinstalled separately if desired.

Also removed the set validation as it was now wrong,
and removed the warning about no Invoke-WebRequest on Core PowerShell
(it is ported now).

I don't like the duplicate parameter logic,
especially around -NoSudo.

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