Type Migration: introducing primitive functional interfaces

[SmirnovOleg]

Hey!

We are a collaborative group of researchers from JetBrains Research and Oregon State University, and we are testing our data-driven plugin, which is based on the IntelliJ's Type Migration framework and adjusts it using custom structural-replace templates that express the adaptations required to perform the type changes.

I want to apply several type changes using it and open the PR, thus introducing primitive functional interfaces in order to prevent unnecessary boxing (like BooleanSupplier instead of Supplier<Boolean>, OptionalInt instead of Optional<Integer>, Predicate<T> instead of Function<T, Boolean>, etc.), since it can affect the performance of the code (Effective Java, Items 44, 61).

This patch is made automatically by the plugin, so it would help us a lot to evaluate the usefulness of our approach!

[SmirnovOleg]

I've reverted commits that affect public methods' signatures (as @akozlova suggested, thanks!). Also, most of the proposed code changes are local, so I hope they do not even need running test suites. Anyway, I've run all tests for the affected packages on my local machine, it passed.