Add function definition notes for missing_named_argument errors (#20794)

This PR helps improve error messages for call argument errors by adding
a note `"foo" is defined in "bar"` to indicates where that called
function is defined
Currently we add it for this error: 
- missing named arguments

In later PRs, I will add this note to the following errors in separate
iterations:
- too few arguments
- too many arguments
- too many positional arguments

Author: KevinRK29

mypy/messages.py

@@ -941,6 +941,7 @@ def too_few_arguments(
     def missing_named_argument(self, callee: CallableType, context: Context, name: str) -> None:
         msg = f'Missing named argument "{name}"' + for_function(callee)
         self.fail(msg, context, code=codes.CALL_ARG)
+        self.note_defined_here(callee, context)
 
     def too_many_arguments(self, callee: CallableType, context: Context) -> None:
         if self.prefer_simple_messages():
@@ -1011,6 +1012,9 @@ def unexpected_keyword_argument(
         self.unexpected_keyword_argument_for_function(
             for_function(callee), name, context, matches=matches
         )
+        self.note_defined_here(callee, context)
+
+    def note_defined_here(self, callee: CallableType, context: Context) -> None:
         module = find_defining_module(self.modules, callee)
         if (
             module

test-data/unit/check-kwargs.test

@@ -480,6 +480,24 @@ tmp/m.py:1: error: Unsupported operand types for + ("int" and "str")
 main:2: error: Unexpected keyword argument "x" for "A"
 main:2: note: "A" defined in "m"
 
+[case testMissingNamedArgumentFromOtherModule]
+import m
+m.f(1)
+m.f(a=1)
+[file m.py]
+def f(a: int, *, b: str) -> None:
+    pass
+[out]
+main:2: error: Missing named argument "b" for "f"
+main:2: note: "f" defined in "m"
+main:3: error: Missing named argument "b" for "f"
+main:3: note: "f" defined in "m"
+
+[case testMissingNamedArgumentForSameModule]
+def f(a: int, *, b: str) -> None:
+    pass
+f(1)  # E: Missing named argument "b" for "f"
+
 [case testStarArgsAndKwArgsSpecialCase]
 from typing import Dict, Mapping