Resolve a Layering Violation in libBasic

Basic should not be allowed to link Parse, yet it was doing so
to allow Version to provide a constructor that would conveniently
parse a StringRef. This entrypoint also emitted diagnostics, so it
pulled in libAST.

Sink the version parser entrypoint down into Parse where it belongs
and point all the clients to the right place.

lib/DriverTool/swift_symbolgraph_extract_main.cpp

@@ -21,6 +21,7 @@
 #include "swift/Frontend/Frontend.h"
 #include "swift/Frontend/PrintingDiagnosticConsumer.h"
 #include "swift/Option/Options.h"
+#include "swift/Parse/ParseVersion.h"
 #include "swift/SymbolGraphGen/SymbolGraphGen.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
@@ -147,8 +148,8 @@ int swift_symbolgraph_extract_main(ArrayRef<const char *> Args,
     using version::Version;
     auto SwiftVersion = A->getValue();
     bool isValid = false;
-    if (auto Version =
-            Version::parseVersionString(SwiftVersion, SourceLoc(), nullptr)) {
+    if (auto Version = VersionParser::parseVersionString(
+            SwiftVersion, SourceLoc(), nullptr)) {
       if (auto Effective = Version.getValue().getEffectiveLanguageVersion()) {
         Invocation.getLangOptions().EffectiveLanguageVersion = *Effective;
         isValid = true;