Move io.opentelemetry.instrumentation.api.servlet to servlet-common

[iNikem]

io.opentelemetry.instrumentation.api.servlet package from instrumentation-api module is used only by servlets and some methods from it are used only from servlet-common module. We can move that package closer to its usage and hide those methods from general public, who should not be concerned with them.

Thoughts? I can do it if get enough support.

[mateuszrzeszutek]

It'd have to be a servlet-bootstrap module - these classes can be (and most likely are) accessed from different classloaders, we have to be certain there's exactly one ContextKey shared between all CLs.

And I'm not sure whether it's a good idea to move all of them out of instrumentation-api - for example, ServerSpanNaming is used in all web/server frameworks that we instrument. It kind of makes sense for it to be present in this module, since updating the server span name is a part of what a web framework instrumentation should do. (Although I think that we should refactor this class so that it sets both the server span name and the http.route attribute)

[trask]

👍 for moving MappingResolver and ServletContextPath, those seem very servlet specific, and then maybe renaming the package from servlet to server

[laurit]

Wouldn't it make sense to split api into public and internal. Internal api could contain classes that are not ready to be used outside the agent like ServerSpanNaming which wouldn't work without bridging context key. Or we could move internal apis under javaagent-bootstrap.