Removing "netcoreapp" and "netfx" TargetGroup (#457)

Removing "netcoreapp"  and "netfx" TargetGroup (#457)

* netcoreapp -> netcoreapp5.0 in .sln files

* netcoreapp; -> netcoreapp5.0;  , netcoreapp- to netcoreapp5.0-

* netcoreapp- -> netcoreapp5.0 in .csproj

* 'netcoreapp -> 'netcoreapp5.0 in .csproj

* done with libraries sub folder

* missed semicolon

* minor changes

* netcoreapp -> netcoreapp5.0 in some extra files

* vNext target variable in configurations.props

* netcoreapp => netcoreapp5/0 in some other .props file

* netcoreapp -> vnext in .csproj

* making the netcorepap framework switch work

* fixing sendToHelix and linux build

* TargetFrameworkVNext -> netcoreappCurrent

* case correct netcoreappcurrent

* fixing send to helix zip path

* netfx -> net472 in .sln

* netfx; -> net472; in .props

* netfx- -> net472- in .props

* netfx - -> net472- in .csproj

* 'netfx-> 'net472 in .csproj

* netfx -> net472 manual change

* fixing ci build for netfx

* Not trying to change the global property

* Fixing build failure due to master changes in net https tests

* adding documentaiton and fixing filtering

* netcoreapp -> netcore5.0 in py file

* changing the path to use netcoreapp5.0 version

* feedback and override corefx path corrected in installers

* remaing netcoreapp5.0 changes done

* netcoreapp-> netcoreapp5.0 after live builds

* net472 -> netframeworkcurrent