Added support for custom object formatters

Custom object formatters allow users to customize how an object is
stringified in matcher failure messages. This can already be done by
adding a `jasmineToString` method to the objects in question. But
it's not always desirable or possible to do that, particularly when
objects of a given "type" do not inherit from a specific prototype.
For instance, suppose a web service returns a list of foos that are
deserialized from JSON, e.g.:

   { fooId: 42, /* more properties */ }

The only way to define `jasmineToString` on those is by writing code to
add it to each instance at runtime. But a custom object formatter can
recognize that the object it's looking at is a foo and format it
accordingly:

   jasmine.addCustomObjectFormatter(function(obj) {
      if (typeof obj.fooId !== 'number') {
            return undefined;
        }

        return '[Foo with ID ' + obj.fooId + ']';
    });

Unlike `jasmineToString`, custom object formatters are scoped to a
particular spec or suite and don't require any changes to the code
under test.

src/core/requireInterface.js

@@ -316,6 +316,20 @@ getJasmineRequireObj().interface = function(jasmine, env) {
     return env.addAsyncMatchers(matchers);
   };
 
+  /**
+   * Add a custom object formatter for the current scope of specs.
+   *
+   * _Note:_ This is only callable from within a {@link beforeEach}, {@link it}, or {@link beforeAll}.
+   * @name jasmine.addCustomObjectFormatter
+   * @since 3.6.0
+   * @function
+   * @param {Function} formatter - A function which takes a value to format and returns a string if it knows how to format it, and `undefined` otherwise.
+   * @see custom_object_formatter
+   */
+  jasmine.addCustomObjectFormatter = function(formatter) {
+    return env.addCustomObjectFormatter(formatter);
+  };
+
   /**
    * Get the currently booted mock {Clock} for this Jasmine environment.
    * @name jasmine.clock