fix: google.protobuf.Any type_url fixes

[nickpestov]

Background

While using protobuf.js we've come across compatibility issues to do with google.protobuf.Any. Namely, when dealing with Any types, according to Google's documentation (referenced below), types.googleapis.com should be used as a default prefix within the type_url. The fromObject function referenced below failed to lookup types that had a prefix in their @type when converting from JSON to protobuf.

Addresses #850.

From Google's google.protobuf.Any docs

// The pack methods provided by protobuf library will by default use
// 'type.googleapis.com/full.type.name' as the type URL and the unpack
// methods only use the fully qualified type name after the last '/'
// in the type URL, for example "foo.bar.com/x/y.z" will yield type
// name "y.z".

And, regarding JSON

// The JSON representation of an `Any` value uses the regular
// representation of the deserialized, embedded message, with an
// additional field `@type` which contains the type URL. Example:
//
//     package google.profile;
//     message Person {
//       string first_name = 1;
//       string last_name = 2;
//     }
//
//     {
//       "@type": "type.googleapis.com/google.profile.Person",
//       "firstName": <string>,
//       "lastName": <string>
//     }
//
// If the embedded message type is well-known and has a custom JSON
// representation, that representation will be embedded adding a field
// `value` which holds the custom JSON in addition to the `@type`
// field. Example (for message [google.protobuf.Duration][]):
//
//     {
//       "@type": "type.googleapis.com/google.protobuf.Duration",
//       "value": "1.212s"
//     }
//

In this PR

• In fromObject, only use type name after the last '/' when doing a lookup and make sure the type_url prefix is preserved. Otherwise, lookups that included type_url path prefixes (such as the default type.googleapis.com prefix) would fail.
• In toObject, use type.googleapis.com default prefix if no type_url prefix is used.
• Adjusted 2 tests to comply with the above and the below statement from Google's docs:

  // * The last segment of the URL's path must represent the fully
  //   qualified name of the type (as in `path/google.protobuf.Duration`).
  //   The name should be in a canonical form (e.g., leading "." is
  //   not accepted).

[kheyse-oqton]

I would love to have this reviewed and merged. I'm currently dealing with the same issue. Thanks for the PR.

[alexander-fenster]

@murgatroid99 I fixed linting problems, this PR is ready to be reviewed now.