Handle `Start-PSBuild -Restore -Runtime ...`
Handle `Start-PSBuild -Restore -Runtime ...`

If a runtime is given, we need to restore for that particular runtime as
well.

This also enables `Warning` `dotnet restore` output, and increases the
verbosity to `Info` if `-Verbose` is used.

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