[ty] Improve the Display for generic type[] types

[AlexWaygood]

Summary

Currently for these types, we throw away their specializations when printing their Displays, e.g.

from typing import Generic, TypeVar

class Foo[T]: ...

S = TypeVar("S")

class Bar(Generic[S]): ...

def _(x: Foo[int], y: Bar[str], z: list[bytes]):
    reveal_type(type(x))  # revealed: type[Foo]
    reveal_type(type(y))  # revealed: type[Bar]
    reveal_type(type(z))  # revealed: type[list]

This PR updates them so that we retain the specialization when printing the Display, if it is a specialized generic class under the hood.

Test Plan

Mdtest added

[github-actions]

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

[github-actions]

mypy_primer results

Changes were detected when running on open source projects

static-frame (https://github.com/static-frame/static-frame)
- static_frame/test/property/strategies.py:927:17: error[invalid-argument-type] Argument to function `get_index_hierarchy` is incorrect: Expected `(...) -> IndexHierarchy`, found `(bound method type[Index].from_labels(labels: Iterable[Unknown], *, /, name: Unknown = None) -> I) | (bound method <class 'Index'>.from_labels(labels: Iterable[Unknown], *, /, name: Unknown = None) -> I)`
+ static_frame/test/property/strategies.py:927:17: error[invalid-argument-type] Argument to function `get_index_hierarchy` is incorrect: Expected `(...) -> IndexHierarchy`, found `(bound method type[Index[Any]].from_labels(labels: Iterable[Unknown], *, /, name: Unknown = None) -> I) | (bound method <class 'Index'>.from_labels(labels: Iterable[Unknown], *, /, name: Unknown = None) -> I)`

No memory usage changes detected ✅

[AlexWaygood]

I think this one's fairly uncontroversial!

[dcreager]

👍 love it