[CS] NFC: Rename CSClosure.cpp -> CSSyntacticElement.cpp

We want to generalize this conjunction logic to
not just be applicable to closures, so rename the
file to match.

Author: hamishknight

lib/Sema/CMakeLists.txt

@@ -3,7 +3,7 @@ add_swift_host_library(swiftSema STATIC
   BuilderTransform.cpp
   CSApply.cpp
   CSBindings.cpp
-  CSClosure.cpp
+  CSSyntacticElement.cpp
   CSGen.cpp
   CSRanking.cpp
   CSSimplify.cpp

lib/Sema/CSClosure.cpp renamed to lib/Sema/CSSyntacticElement.cpp

@@ -1,18 +1,18 @@
-//===--- CSClosure.cpp - Closures -----------------------------------------===//
+//===--- CSSyntacticElement.cpp - Syntactic Element Constraints -----------===//
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 //===----------------------------------------------------------------------===//
 //
-// This file implements constraint generation and solution application for
-// closures. It provides part of the implementation of the ConstraintSystem
-// class.
+// This file implements SyntacticElement constraint generation and solution
+// application, which is used to type-check the bodies of closures. It provides
+// part of the implementation of the ConstraintSystem class.
 //
 //===----------------------------------------------------------------------===//