[red-knot] Support calling a typing.Callable (#16888)

## Summary

Part of #15382, this PR adds support for calling a variable that's
annotated with `typing.Callable`.

## Test Plan

Add test cases in a new `call/annotation.md` file.

crates/red_knot_python_semantic/resources/mdtest/annotations/unsupported_special_forms.md

@@ -29,8 +29,6 @@ def i(callback: Callable[Concatenate[int, P], R_co], *args: P.args, **kwargs: P.
     # TODO: should understand the annotation
     reveal_type(kwargs)  # revealed: dict
 
-    # TODO: not an error; remove once `call` is implemented for `Callable`
-    # error: [call-non-callable]
     return callback(42, *args, **kwargs)
 
 class Foo:

crates/red_knot_python_semantic/resources/mdtest/call/annotation.md

@@ -0,0 +1,43 @@
+# `typing.Callable`
+
+```py
+from typing import Callable
+
+def _(c: Callable[[], int]):
+    reveal_type(c())  # revealed: int
+
+def _(c: Callable[[int, str], int]):
+    reveal_type(c(1, "a"))  # revealed: int
+
+    # error: [invalid-argument-type] "Object of type `Literal["a"]` cannot be assigned to parameter 1; expected type `int`"
+    # error: [invalid-argument-type] "Object of type `Literal[1]` cannot be assigned to parameter 2; expected type `str`"
+    reveal_type(c("a", 1))  # revealed: int
+```
+
+The `Callable` annotation can only be used to describe positional-only parameters.
+
+```py
+def _(c: Callable[[int, str], None]):
+    # error: [unknown-argument] "Argument `a` does not match any known parameter"
+    # error: [unknown-argument] "Argument `b` does not match any known parameter"
+    # error: [missing-argument] "No arguments provided for required parameters 1, 2"
+    reveal_type(c(a=1, b="b"))  # revealed: None
+```
+
+If the annotation uses a gradual form (`...`) for the parameter list, then it can accept any kind of
+parameter with any type.
+
+```py
+def _(c: Callable[..., int]):
+    reveal_type(c())  # revealed: int
+    reveal_type(c(1))  # revealed: int
+    reveal_type(c(1, "str", False, a=[1, 2], b=(3, 4)))  # revealed: int
+```
+
+An invalid `Callable` form can accept any parameters and will return `Unknown`.
+
+```py
+# error: [invalid-type-form]
+def _(c: Callable[42, str]):
+    reveal_type(c())  # revealed: Unknown
+```