Test protocol stubs for mutating getters

Author: AnthonyLatsis

test/decl/protocol/conforms/Inputs/fixit_stub_mutability_proto_module.swift

@@ -1,4 +1,4 @@
 public protocol ExternalMutabilityProto {
     mutating func foo()
-    subscript() -> Int { get nonmutating set }
+    subscript() -> Int { mutating get nonmutating set }
 }

test/decl/protocol/conforms/fixit_stub_editor.swift

@@ -55,5 +55,5 @@ import fixit_stub_mutability_proto_module
 class Class2: ExternalMutabilityProto { // expected-error{{type 'Class2' does not conform to protocol 'ExternalMutabilityProto'}} expected-note{{do you want to add protocol stubs?}} {{40-40=\n    func foo() {\n        <#code#>\n    \}\n\n    subscript() -> Int {\n        get {\n            <#code#>\n        \}\n        set(newValue) {\n            <#code#>\n        \}\n    \}\n}}
 }
 
-struct Struct2: ExternalMutabilityProto { // expected-error{{type 'Struct2' does not conform to protocol 'ExternalMutabilityProto'}} expected-note{{do you want to add protocol stubs?}} {{42-42=\n    mutating func foo() {\n        <#code#>\n    \}\n\n    subscript() -> Int {\n        get {\n            <#code#>\n        \}\n        nonmutating set(newValue) {\n            <#code#>\n        \}\n    \}\n}}
+struct Struct2: ExternalMutabilityProto { // expected-error{{type 'Struct2' does not conform to protocol 'ExternalMutabilityProto'}} expected-note{{do you want to add protocol stubs?}} {{42-42=\n    mutating func foo() {\n        <#code#>\n    \}\n\n    subscript() -> Int {\n        mutating get {\n            <#code#>\n        \}\n        nonmutating set(newValue) {\n            <#code#>\n        \}\n    \}\n}}
 }