[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

crates/ty_ide/src/goto_declaration.rs

@@ -123,6 +123,23 @@ mod tests {
           |
         4 |         pass
         5 |
+        6 | instance = MyClass()
+          |            ^^^^^^^
+          |
+
+        info[goto-declaration]: Declaration
+         --> main.py:3:9
+          |
+        2 | class MyClass:
+        3 |     def __init__(self):
+          |         ^^^^^^^^
+        4 |         pass
+          |
+        info: Source
+         --> main.py:6:12
+          |
+        4 |         pass
+        5 |
         6 | instance = MyClass()
           |            ^^^^^^^
           |