Compilation with no constructor properties

[Drew Hamilton]

Currently, an empty primary constructor successfully compiles. However, it later causes R8 to error (in Android projects).

Figure out if this is producing invalid bytecode or if something else is wrong. More importantly, define the correct behavior for this use case. Favor disallowing it, like data classes do.

Also consider what to do for non-empty primary constructors with no properties (only plain parameters).