Move private APIs to private namespace

Fixes #2078

src/core/buildExpectationResult.js

@@ -1,7 +1,7 @@
 //TODO: expectation result may make more sense as a presentation of an expectation.
 getJasmineRequireObj().buildExpectationResult = function(j$) {
   function buildExpectationResult(options) {
-    const exceptionFormatter = new j$.ExceptionFormatter();
+    const exceptionFormatter = new j$.private.ExceptionFormatter();
 
     /**
      * Describes the result of evaluating an expectation
@@ -24,7 +24,7 @@ getJasmineRequireObj().buildExpectationResult = function(j$) {
     };
 
     if (!result.passed) {
-      if (options.error && !j$.isString_(options.error)) {
+      if (options.error && !j$.private.isString(options.error)) {
         if ('code' in options.error) {
           result.code = options.error.code;
         }