Accept multiline quoted annotations (#16765)

See discussion in
https://discuss.python.org/t/newlines-within-triple-quoted-type-expressions/42833

Author: hauntsaninja

mypy/fastparse.py

@@ -318,7 +318,7 @@ def parse_type_string(
     string expression "blah" using this function.
     """
     try:
-        _, node = parse_type_comment(expr_string.strip(), line=line, column=column, errors=None)
+        _, node = parse_type_comment(f"({expr_string})", line=line, column=column, errors=None)
         if isinstance(node, UnboundType) and node.original_str_expr is None:
             node.original_str_expr = expr_string
             node.original_str_fallback = expr_fallback_name

test-data/unit/check-basic.test

@@ -502,3 +502,19 @@ s2: str = 42  # E: Incompatible types in assignment (expression has type "int",
 s3: str = 42  # E: Incompatible types in assignment (expression has type "int", variable has type "str")
 [file c.py]
 s3: str = 'foo'
+
+[case testMultilineQuotedAnnotation]
+x: """
+
+   int |
+   str
+
+"""
+reveal_type(x)  # N: Revealed type is "Union[builtins.int, builtins.str]"
+
+y: """(
+    int |
+    str
+)
+"""
+reveal_type(y)  # N: Revealed type is "Union[builtins.int, builtins.str]"