PY-16055 Add quickfix and tests for functions with incorrect return annotation

Add quickfix for functions whose return type doesn't match their annotated type.

python/testData/quickFixes/PyMakeFunctionReturnTypeQuickFixTest/oneReturn.py

@@ -0,0 +1,3 @@
+def f(x):
+    # type: (int) -> str
+    return <warning descr="Expected type 'str', got 'int' instead">42<caret></warning>

python/testData/quickFixes/PyMakeFunctionReturnTypeQuickFixTest/oneReturn_after.py

@@ -0,0 +1,3 @@
+def f(x):
+    # type: (int) -> int
+    return 42

python/testData/quickFixes/PyMakeFunctionReturnTypeQuickFixTest/py3OneReturn.py

@@ -0,0 +1,2 @@
+def f(x) -> str:
+    return <warning descr="Expected type 'str', got 'int' instead">42<caret></warning>

python/testData/quickFixes/PyMakeFunctionReturnTypeQuickFixTest/py3OneReturn_after.py

@@ -0,0 +1,2 @@
+def f(x) -> int:
+    return 42