[sdk-api-digester] Record whether a value decl is static.

Changing a static member to a non-static one, or the other way around,
can be source-breaking.

test/api-digester/Inputs/cake.swift

@@ -1,5 +1,5 @@
 public struct S1 {
-  public func foo1() {}
+  public static func foo1() {}
   mutating public func foo2() {}
   internal func foo3() {}
   private func foo4() {}
@@ -7,5 +7,5 @@ public struct S1 {
 }
 
 public class C1 {
-	open func foo1() {}
+	open class func foo1() {}
 }

test/api-digester/Outputs/cake.json

@@ -17,9 +17,10 @@
           "name": "foo1",
           "printedName": "foo1()",
           "declKind": "Func",
-          "usr": "s:FV4cake2S14foo1FT_T_",
+          "usr": "s:ZFV4cake2S14foo1FT_T_",
           "location": "",
           "moduleName": "cake",
+          "static": true,
           "children": [
             {
               "kind": "TypeNominal",
@@ -77,9 +78,10 @@
           "name": "foo1",
           "printedName": "foo1()",
           "declKind": "Func",
-          "usr": "s:FC4cake2C14foo1FT_T_",
+          "usr": "s:ZFC4cake2C14foo1FT_T_",
           "location": "",
           "moduleName": "cake",
+          "static": true,
           "children": [
             {
               "kind": "TypeNominal",

tools/swift-api-digester/DigesterEnums.def

@@ -68,6 +68,7 @@ KEY(printedName)
 KEY(moduleName)
 KEY(throwing)
 KEY(mutating)
+KEY(static)
 KEY(typeAttributes)
 KEY(declAttributes)
 KEY(declKind)

tools/swift-api-digester/swift-api-digester.cpp

@@ -265,6 +265,7 @@ struct SDKNodeInitInfo {
   StringRef ModuleName;
   bool IsThrowing = false;
   bool IsMutating = false;
+  bool IsStatic = false;
   Optional<uint8_t> SelfIndex;
   std::vector<SDKDeclAttrKind> DeclAttrs;
   std::vector<TypeAttrKind> TypeAttrs;
@@ -326,12 +327,14 @@ class SDKNodeDecl : public SDKNode {
   StringRef Location;
   StringRef ModuleName;
   std::vector<SDKDeclAttrKind> DeclAttributes;
+  bool IsStatic;
   bool hasDeclAttribute(SDKDeclAttrKind DAKind) const;
 
 protected:
   SDKNodeDecl(SDKNodeInitInfo Info, SDKNodeKind Kind) : SDKNode(Info, Kind),
     DKind(Info.DKind), Usr(Info.USR), Location(Info.Location),
-                  ModuleName(Info.ModuleName), DeclAttributes(Info.DeclAttrs) {}
+    ModuleName(Info.ModuleName), DeclAttributes(Info.DeclAttrs),
+    IsStatic(Info.IsStatic) {}
 
 public:
   StringRef getUsr() const { return Usr; }
@@ -346,6 +349,7 @@ public:
   StringRef getFullyQualifiedName();
   bool isSDKPrivate();
   bool isDeprecated();
+  bool isStatic() const { return IsStatic; };
 };
 
 class SDKNodeType : public SDKNode {
@@ -774,6 +778,8 @@ NodeUniquePtr SDKNode::constructSDKNode(llvm::yaml::MappingNode *Node) {
       Info.IsThrowing = true;
     } else if (Key == Key_mutating) {
       Info.IsMutating = true;
+    } else if (Key == Key_static) {
+      Info.IsStatic = true;
     } else if (Key == Key_typeAttributes) {
       auto *Seq = cast<llvm::yaml::SequenceNode>(Pair.getValue());
       for (auto It = Seq->begin(); It != Seq->end(); ++ It) {
@@ -1009,7 +1015,7 @@ SDKNodeInitInfo::SDKNodeInitInfo(ValueDecl *VD) :
     USR(calculateUsr(VD)), Location(calculateLocation(VD)),
     ModuleName(VD->getModuleContext()->getName().str()),
     IsThrowing(isFuncThrowing(VD)), IsMutating(isFuncMutating(VD)),
-    SelfIndex(getSelfIndex(VD)) {
+    IsStatic(VD->isStatic()), SelfIndex(getSelfIndex(VD)) {
   if (VD->getAttrs().getDeprecated(VD->getASTContext()))
     DeclAttrs.push_back(SDKDeclAttrKind::DAK_deprecated);
 }
@@ -1345,6 +1351,8 @@ namespace swift {
           out.mapRequired(Key_usr, Usr);
           out.mapRequired(Key_location, Location);
           out.mapRequired(Key_moduleName, ModuleName);
+          if (auto isStatic = D->isStatic())
+            out.mapRequired(Key_static, isStatic);
 
           if (auto F = dyn_cast<SDKNodeAbstractFunc>(value.get())) {
             if (bool isThrowing = F->isThrowing())