Implement support for property builders

[ZacSweers]

Resolves #79

[adamsp]

I'm not sure how close to the original you want to fly here - what you have will work for existing implementations, but will behave differently than AutoValue if users make calls in the wrong order.

We're also missing the chained builder calls from the docs:

Edit: I suppose the remainingMethods TODOs will solve the chained builder calls, since those aren't generated anyway.

[adamsp]

This implementation doesn't match the docs - I think we need to check if the member is null first:

The same caller can mix the two styles only in limited ways; once foosBuilder has been called, any subsequent call to setFoos will throw an unchecked exception. On the other hand, calling setFoos first is okay; a later call to foosBuilder will return a builder already populated with the previously-supplied elements.

Like this:

    @Override
    public FakeComment.Builder reactions(ImmutableList<Reaction> reactions) {
      if (reactions == null) {
        throw new NullPointerException("Null reactions");
      }
      if (reactionsBuilder$ != null) {
        throw new IllegalStateException("Cannot set reactions after calling reactionsBuilder()");
      }
      this.reactions = reactions;
      return this;
    }

[ZacSweers]

oooo good catch, let me update

[ZacSweers]

abf0f1b

[ZacSweers]

for chained builders - isn't the doc saying to manually write those and just hide the abstract builder method?

[ZacSweers]

I think I need to update for this case as well

On the other hand, calling setFoos first is okay; a later call to foosBuilder will return a builder already populated with the previously-supplied elements.

Interestingly though, the generated code I see in AV doesn't appear to do this

[ZacSweers]

Ahhh it's only if a setter is present