(cherry picked from commit 1ec98c23)

Since it's possible for certain dispatchers to completely avoid yielding, and currently the immediate dispatchers exhibit this behavior, we need an alternate mechanism of forcing suspension or UndeclaredThrowableExceptions will still be seen.

Retrofit does not have its own thread pool onto which we can defer resuming. Instead we rely to Dispatchers.Default and forcibly suspend the caller using low-level coroutine intrinsics.

(cherry picked from commit 9d683b75)

(cherry picked from commit 02343da2)

Because of a race condition caused by thread preemption, this can sometimes happen. Explicitly yield to ensure the exception is delivered asynchronously to the continuation.

(cherry picked from commit 60c92e37)

(cherry picked from commit 06978ccd)

(cherry picked from commit 5c662020)

Add JAXB Converter in Document

Functionally does nothing, just somewhat cleaner to be able to do `baseUrl(URL)` than `baseUrl(URL#toString());` if handling a `URL` rather than `String`.
Used `HttpUrl.get(String)` as `HttpUrl.get(URL)` returns null instead of throwing an exception.

Support okhttp3.Headers for HeadersMap parameters.

Next version is 2.6.0

Also fix some Javadoc errors and ensure Javadoc (and source) jar generation is tested on CI.

Update to Gson 2.8.5.

Fix support for protobuf 3.5+

Remove use of Mockito

It wasn't used for anything interesting and I prefer not having it around to tempt contributors to add new usages of it.

Add some missing @Nullable annotations to Utils

Back suspend methods with the CallAdapter for Call.

This allows the regular mechanism of composition of behavior without explicitly needing to model suspending functions in the API.

Add annotation for skipping the callback executor