Add support for dialyzer --incremental when available

[TD5]

When the environment's OTP version supports dialyzer --incremental (see the PR introducing it), enable an --incremental/-i option to rebar3 dialyzer in order to make it accessible.

In erlang/otp#5997, we added an --incremental option to Dialyzer, however, in order to make good use of it from a rebar3 project, you'd probably want to have a corresponding option in rebar3 dialyzer, which is what I've added here.

This PR introduces quite a bare-bones option, since you could do more in terms of reading incrementality-specific metrics from Dialyzer and reporting them, but it at least allows some early experimentation when it detects an appropriate bleeding-edge OTP version with the necessary features. For older OTP versions, users won't see this option, so nothing should change from their perspective.

As a point of comparison, when running on the rebar3 project itself, running Dialyzer the usual way without incrementality, the first run takes 2.25 mins, and a second run takes 25 secs. When using --incremental, it takes 1.5 mins, going down to 6 seconds on a re-run. Of course, your milage will very definitely vary depending on machine's performance/load, the changes you make between Dialyzer analyses, and the structure of the project you run it on.

N.B. I also clarified the Resolving files... log line, since before it sort of implied the same work was being done twice, which isn't a good look for an "incremental" mode 😉

[ferd]

Looks like a good idea. A test may be tricky to put in place but worth it (maybe behind a version/dynamic switch). It seems like Dialyzer is failing on OTP-25. Not sure why, I'm assuming the typing is blowing up because of unsupported options? may be worth ignoring warnings if that's the actual reason.

[TD5]

I'm assuming the typing is blowing up because of unsupported options

Yes, this is the case. I've got a PR I am about to submit to OTP to resolve that part. (EDIT: see erlang/otp#6207)

A test may be tricky to put in place but worth it

I agree, I'll see what I can do.

[TD5]

Okay, I've suppressed that Dialyzer warning for now, and commented next to it with a link to the PR to fix it. I've also added unit tests around incremental mode which are skipped if the current OTP version does not support incrementality.

[TD5]

@ferd, what are your thoughts on the state of this PR now?