[analyzer] Dump the environment entry kind as well

[steakhal]

Summary

By this change the exploded-graph-rewriter will display the class kind
of the expression of the environment entry. It makes easier to decide if
the given entry corresponds to the lvalue or to the rvalue of some
expression.

It turns out the rewriter already had support for visualizing it, but
probably was never actually used?

Example rewritten-dump after my change:

Note the same pretty representation; now it's clear at first glance which is which.

[martong]

LGTM

clang/lib/StaticAnalyzer/Core/Environment.cpp

LCtx->printJson(Out, NL, Space, IsDot, [&](const LocationContext *LC) {
 
     for (BindingsTy::iterator I = ExprBindings.begin(); I != ExprBindings.end();
          ++I) {
       if (I->first.getLocationContext() != LC)
         continue;
 
       const Stmt *S = I->first.getStmt();
       Indent(Out, InnerSpace, IsDot)
-          << "{ \"stmt_id\": " << S->getID(Ctx) << ", \"pretty\": ";
+          << "{ \"stmt_id\": " << S->getID(Ctx) << ", \"kind\": \""
+          << S->getStmtClassName() << "\", \"pretty\": ";
       S->printJson(Out, nullptr, PP, /*AddQuotes=*/true);
 
       Out << ", \"value\": ";
       I->second.printJson(Out, /*AddQuotes=*/true);
 
       Out << " }";
 
       if (I != LastI)

clang/test/Analysis/expr-inspection.c

 // CHECK:      "program_state": {
 // CHECK-NEXT:   "store": { "pointer": "{{0x[0-9a-f]+}}", "items": [
 // CHECK-NEXT:     { "cluster": "y", "pointer": "{{0x[0-9a-f]+}}", "items": [
 // CHECK-NEXT:       { "kind": "Direct", "offset": {{[0-9]+}}, "value": "2 S32b" }
 // CHECK-NEXT:     ]}
 // CHECK-NEXT:   ]},
 // CHECK-NEXT:   "environment": { "pointer": "{{0x[0-9a-f]+}}", "items": [
 // CHECK-NEXT:     { "lctx_id": {{[0-9]+}}, "location_context": "#0 Call", "calling": "foo", "location": null, "items": [
-// CHECK-NEXT:       { "stmt_id": {{[0-9]+}}, "pretty": "clang_analyzer_printState", "value": "&code{clang_analyzer_printState}" }
+// CHECK-NEXT:       { "stmt_id": {{[0-9]+}}, "kind": "ImplicitCastExpr", "pretty": "clang_analyzer_printState", "value": "&code{clang_analyzer_printState}" }
 // CHECK-NEXT:     ]}
 // CHECK-NEXT:   ]},
 // CHECK-NEXT:   "constraints": [
 // CHECK-NEXT:     { "symbol": "reg_$0<int x>", "range": "{ [-2147483648, 13] }" }
 // CHECK-NEXT:   ],
 // CHECK-NEXT:   "equivalence_classes": null,
 // CHECK-NEXT:   "disequality_info": null,
 // CHECK-NEXT:   "dynamic_types": null,