Migrate to better type inference tooling to detect BC breaks in types

[Ocramius]

As documented in #134, type inference based on documented types is weak.

In practice, we want to detect type variance changes for complex types, such as @var Foo<Bar, Baz>.

We also want to detect changes such as:

function foo() {
-    return 1;
+    return 'foo';
}

These types are currently not inferred (BC check completely skipped), and that is a problem.

I think @psalm could help with this, but need to inspect further.

[Ocramius]

As discussed with @muglug, there is some internal API in Psalm that could be helpful here (but is not covered by BC yet):

• there’s this method for params: https://github.com/vimeo/psalm/blob/210a0fc98d0d905394ff23e2ee2be6a1090cbac6/src/Psalm/Internal/Codebase/Methods.php#L294-L305
• and this method for method return types: https://github.com/vimeo/psalm/blob/210a0fc98d0d905394ff23e2ee2be6a1090cbac6/src/Psalm/Internal/Codebase/Methods.php#L531-L538
• and this for property types: https://github.com/vimeo/psalm/blob/210a0fc98d0d905394ff23e2ee2be6a1090cbac6/src/Psalm/Internal/Codebase/Properties.php#L225-L235