[AST] Get it a deterministic traverse order

Replace `DenseMap` for `std::map` for deterministic traversing order.
This allows deterministic iteration order for top level decl and class
members, and allows producing deterministic swiftdeps output.

rdar://147513165

Author: cachemeifyoucan

lib/AST/Module.cpp

@@ -147,7 +147,7 @@ class swift::SourceLookupCache {
   /// A lookup map for value decls. When declarations are added they are added
   /// under all variants of the name they can be found under.
   class ValueDeclMap {
-    llvm::DenseMap<DeclName, TinyPtrVector<ValueDecl *>> Members;
+    std::map<DeclName, TinyPtrVector<ValueDecl *>> Members;
 
   public:
     void add(ValueDecl *VD) {
@@ -161,7 +161,7 @@ class swift::SourceLookupCache {
     }
 
     void clear() {
-      Members.shrink_and_clear();
+      Members.clear();
     }
 
     decltype(Members)::const_iterator begin() const { return Members.begin(); }

test/Frontend/output_determinism_check.swift

@@ -38,3 +38,28 @@
 
 public var x = 1
 public func test() {}
+
+class A {
+  var a = 0
+  var b = 0
+  var c = 0
+  var d = 0
+}
+class B {
+  var a = 0
+  var b = 0
+  var c = 0
+  var d = 0
+}
+class C {
+  var a = 0
+  var b = 0
+  var c = 0
+  var d = 0
+}
+class D {
+  var a = 0
+  var b = 0
+  var c = 0
+  var d = 0
+}