Merge pull request #59530 from apple/egorzhdan/clangimporter-synthesizer-nfc

[ClangImporter] NFC: extract Swift decl synthesis logic into a separate file

Author: egorzhdan

lib/ClangImporter/CMakeLists.txt

@@ -13,6 +13,7 @@ add_swift_host_library(swiftClangImporter STATIC
   ClangImporterRequests.cpp
   ClangModuleDependencyScanner.cpp
   ClangSourceBufferImporter.cpp
+  SwiftDeclSynthesizer.cpp
   DWARFImporter.cpp
   ImportDecl.cpp
   ImportEnumInfo.cpp