[release/7.0] source-build: support building aspnetcore using non-portable runtime packages. (#44978)

- source-build: support building aspnetcore using non-portable runtime packages.
  - Currently source-build performs 'runtime-portable' build that produces 'linux-{arch}' packages that are
  used when building ASP.NET Core.
  - With this change, we can use the non-portable packages that are produced by the source-build 'runtime'
  build, and eliminate the 'runtime-portable' build.
- Invert PortableBuild checks.
- Revert name change.

Co-authored-by: Tom Deseyn <tom.deseyn@gmail.com>