Improve the `help()` of type alias objects

Feature or enhancement

EDIT: See https://discuss.python.org/t/runtime-docstrings-for-type-aliases/108901

Proposal:

Consider recording __doc__ on type alias objects.

For instance:

type Pair[T] = tuple[T, T]
"""A pair of values of the same type."""

Now Pair.__doc__ is "A pair of values of the same type.".

Use it in the REPL:

>>> from mymodule import Pair
>>> help(Pair)
Help on type alias Pair in module mymodule:

Pair[T] = tuple[T, T]
 |  A pair of values of the same type.
 |
 |  Attributes:
 |
 |  __value__
 |      Lazily evaluated value of the type alias.
 |
 |  evaluate_value
 |      Evaluation function for __value__.
 |
 |  __type_params__
 |      Type parameters declared by the type alias.
 |
 |  __parameters__
 |      Type parameters after expansion.
 |
 |  __name__
 |      Name of the type alias.
 |
 |  __qualname__
 |      Qualified name of the type alias.
 |
 |  __module__
 |      Module in which the type alias was defined.

(I wrote this text by hand, the actual thing could probably be improved.)
I assume IDEs/LSPs already catch it, so this is mainly a runtime feature.

Current help() just shows a slightly confusing help on the type alias type itself:

>>> type x = int
>>> help(x)
Help on TypeAliasType in module __main__ object:

x = class TypeAliasType(builtins.object)
 |  Type alias.
 |
 |  Type aliases are created through the type statement::
 |
...

It is confusing because (1) it reads like TypeAliasType was defined in __main__ (Help on TypeAliasType in module __main__ object), and (2) almost like if i did x = typing.TypeAliasType. (Which could be improved on its own? We could instead say x = instance of class ..., not just x = class ...)

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

首先在 REPL 中重现类型别名的当前 help(x) 输出，然后跟踪 help() 对类型别名对象的处理以及运行时类型别名的实现。当能够记录运行时文档字符串，并且 help(Pair) 能够呈现该别名、其文档和相关属性，而不会误导性地将该别名描述为 TypeAliasType 类时，即表示完成。