[clang][dataflow] Extend debug output for Environment. (llvm#79982)

*  Print `ReturnLoc`, `ReturnVal`, and `ThisPointeeLoc` if applicable.

* For entries in `LocToVal` that correspond to declarations, print the
names
   of the declarations next to them.

I've removed the FIXME because all relevant fields are now being dumped.
I'm
not sure we actually need the capability for the caller to specify which
fields
to dump, so I've simply deleted this part of the comment.

Some examples of the output:


![image](https://github.com/llvm/llvm-project/assets/29098113/17d0978f-b86d-4555-8a61-d1f2021f8d59)


![image](https://github.com/llvm/llvm-project/assets/29098113/021dbb24-5fe2-4720-8a08-f48dcf4b88f8)

clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp

@@ -1009,12 +1009,15 @@ bool Environment::allows(const Formula &F) const {
 }
 
 void Environment::dump(raw_ostream &OS) const {
-  // FIXME: add printing for remaining fields and allow caller to decide what
-  // fields are printed.
-  OS << "DeclToLoc:\n";
-  for (auto [D, L] : DeclToLoc)
-    OS << "  [" << D->getNameAsString() << ", " << L << "]\n";
+  llvm::DenseMap<const StorageLocation *, std::string> LocToName;
+  if (ThisPointeeLoc != nullptr)
+    LocToName[ThisPointeeLoc] = "this";
 
+  OS << "DeclToLoc:\n";
+  for (auto [D, L] : DeclToLoc) {
+    auto Iter = LocToName.insert({L, D->getNameAsString()}).first;
+    OS << "  [" << Iter->second << ", " << L << "]\n";
+  }
   OS << "ExprToLoc:\n";
   for (auto [E, L] : ExprToLoc)
     OS << "  [" << E << ", " << L << "]\n";
@@ -1025,7 +1028,28 @@ void Environment::dump(raw_ostream &OS) const {
 
   OS << "LocToVal:\n";
   for (auto [L, V] : LocToVal) {
-    OS << "  [" << L << ", " << V << ": " << *V << "]\n";
+    OS << "  [" << L;
+    if (auto Iter = LocToName.find(L); Iter != LocToName.end())
+      OS << " (" << Iter->second << ")";
+    OS << ", " << V << ": " << *V << "]\n";
+  }
+
+  if (const FunctionDecl *Func = getCurrentFunc()) {
+    if (Func->getReturnType()->isReferenceType()) {
+      OS << "ReturnLoc: " << ReturnLoc;
+      if (auto Iter = LocToName.find(ReturnLoc); Iter != LocToName.end())
+        OS << " (" << Iter->second << ")";
+      OS << "\n";
+    } else if (!Func->getReturnType()->isVoidType()) {
+      if (ReturnVal == nullptr)
+        OS << "ReturnVal: nullptr\n";
+      else
+        OS << "ReturnVal: " << *ReturnVal << "\n";
+    }
+
+    if (isa<CXXMethodDecl>(Func)) {
+      OS << "ThisPointeeLoc: " << ThisPointeeLoc << "\n";
+    }
   }
 
   OS << "\n";