Add #include "swift/Basic/Assertions.h" to a lot of source files

Although I don't plan to bring over new assertions wholesale
into the current qualification branch, it's entirely possible
that various minor changes in main will use the new assertions;
having this basic support in the release branch will simplify that.
(This is why I'm adding the includes as a separate pass from
rewriting the individual assertions)

lib/DependencyScan/ModuleDependencyScanner.cpp

@@ -19,6 +19,7 @@
 #include "swift/AST/ModuleLoader.h"
 #include "swift/AST/SourceFile.h"
 #include "swift/AST/TypeCheckRequests.h"
+#include "swift/Basic/Assertions.h"
 #include "swift/Basic/FileTypes.h"
 #include "swift/Basic/PrettyStackTrace.h"
 #include "swift/ClangImporter/ClangImporter.h"