[cxx-interop] Use the locations imported from C++

A recent PR (#77204) started to import C++ source locations into Swift.
This PR flips a switch so these locations are actually used more widely.

Author: Gabor Horvath

lib/AST/Decl.cpp

@@ -1011,6 +1011,7 @@ static_assert(sizeof(checkSourceLocType(&ID##Decl::getLoc)) == 2, \
     return getLocFromSource();
   switch(File->getKind()) {
   case FileUnitKind::Source:
+  case FileUnitKind::ClangModule:
     return getLocFromSource();
   case FileUnitKind::SerializedAST: {
     if (!SerializedOK)
@@ -1019,7 +1020,6 @@ static_assert(sizeof(checkSourceLocType(&ID##Decl::getLoc)) == 2, \
   }
   case FileUnitKind::Builtin:
   case FileUnitKind::Synthesized:
-  case FileUnitKind::ClangModule:
   case FileUnitKind::DWARFModule:
     return SourceLoc();
   }

test/Interop/Cxx/class/nonescapable-errors.swift

@@ -48,6 +48,7 @@ public func noAnnotations() -> View {
     // CHECK-NOT: nonescapable.h:19
     f2(nil, nil)
     // CHECK: nonescapable.h:23:6: warning: the returned type 'View' is annotated as non-escapable; its lifetime dependencies must be annotated
+    // CHECKL nonescapable.h:23:6: error: cannot infer lifetime dependence, no parameters found that are either ~Escapable or Escapable with a borrowing ownership
     g(nil)
     return View()
 }