Using top-level wildcard for `kotlin_package_mapping` should not rewrite well-known type package

[darronschall]

If I use the kotlin_package_mapping feature with a top-level wildcard (to move all of the proto packages underneath my own top-level package), like this:

kotlin_package_mapping="*->com.exampleapp.api.*"

The generated code will convert well-known-types incorrectly. That is, it converts google.protobuf.Timestamp to com.exampleapp.api.pbandk.wkt.Timestamp. The results in a compiler error; the pbandk.wkt.Timestamp is provided by the PBandK library itself and not available at the mapped package.

The workaround is to preserve the well-known-type package mapping, like this:

kotlin_package_mapping="google.protobuf->pbandk.wkt;*->com.exampleapp.api.*"

At first I thought this was a bug, but considering I did ask every package to be rewritten to a new top-level package, maybe it's working as designed? I figured I'd log it just in case.