Specialize empty collections to Any as a fallback

Context

I have a pending PR for typeshed which fixes overparameterized dict.get and dict.pop methods: python/typeshed#10294. The PR causes a lot of failures in various GitHub projects due to how mypy treats empty collections. Specifically, if dict.get is annotated as

class dict(Generic[KT, VT]):
    def get(self, key: KT, default: T) -> T | VT: ...

mypy infers the type of v in

def test(d: dict[str, Any]):
    v = d.get("foo", {})

to be Any | dict[<unknown>, <unknown>], instead of Any | dict[Any, Any].

Feature

Specialize empty collections to Any if no other information is available to recover type arguments.

Pitch

Using <unknown> instead of Any requires users to cast or add type annotations where they otherwise will not be necessary. See comments in the PR for a few examples from real projects.

Start by reproducing the shown dict.get example in mypy and inspect how empty collection expressions are inferred when no type arguments can be recovered. Done means empty collections in this situation are specialized to Any rather than unknown, while the behavior remains covered by relevant type-checking tests.