[CMake] Add back 'SwiftSyntaxConfig.cmake' exported targets

And remove SwiftSyntaxTargets.cmake because it was just a duplication.

Author: rintaro

CMakeLists.txt

@@ -97,10 +97,4 @@ if (SWIFTSYNTAX_ENABLE_ASSERTIONS)
 endif()
 
 add_subdirectory(Sources)
-
-if(PROJECT_IS_TOP_LEVEL)
-  export(EXPORT SwiftSyntaxTargets
-         FILE "${CMAKE_CURRENT_BINARY_DIR}/cmake/SwiftSyntaxTargets.cmake"
-         NAMESPACE SwiftSyntax::
-  )
-endif()
+add_subdirectory(cmake/modules)

cmake/modules/CMakeLists.txt

@@ -0,0 +1,5 @@
+if(PROJECT_IS_TOP_LEVEL)
+  export(EXPORT SwiftSyntaxTargets
+         FILE ${CMAKE_CURRENT_BINARY_DIR}/SwiftSyntaxConfig.cmake
+         NAMESPACE SwiftSyntax::)
+endif()