[ty] Make initializer calls GotoTargets (#20014)
This introduces `GotoTarget::Call` that represents the kind of
ambiguous/overloaded click of a callable-being-called:
```py
x = mymodule.MyClass(1, 2)
^^^^^^^
```
This is equivalent to `GotoTarget::Expression` for the same span but
enriched
with information about the actual callable implementation.
That is, if you click on `MyClass` in `MyClass()` it is *both* a
reference to the class and to the initializer of the class. Therefore
it would be ideal for goto-* and docstrings to be some intelligent
merging of both the class and the initializer.
In particular the callable-implementation (initializer) is prioritized
over the callable-itself (class) so when showing docstrings we will
preferentially show the docs of the initializer if it exists, and then
fallback to the docs of the class.
For goto-definition/goto-declaration we will yield both the class and
the initializer, requiring you to pick which you want (this is perhaps
needlessly pedantic but...).
Fixes https://github.com/astral-sh/ty/issues/898
Fixes https://github.com/astral-sh/ty/issues/1010
