Add version flag and version info in generated code

[meling]

Fixes #1216.

Example output (edited):

"use strict";
/**
 * @fileoverview gRPC-Web generated client stub for ag
 * @enhanceable
 * @public
 */
exports.__esModule = true;
exports.AutograderServiceClient = void 0;
// Code generated by protoc-gen-grpc-web. DO NOT EDIT.
// versions:
//  protoc-gen-grpc-web v1.3.1
//  protoc              v3.19.4
// source: ag/ag.proto
/* eslint-disable */
// @ts-nocheck

Caveat: Needs manual updating of newly added version.h file. The process of deciding the version number is not clear to me, and whether or not it could be automated somehow.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: meling / name: Hein Meling (67da097, c91e785)

[sampajano]

@meling Thanks so much for the change!! Much appreciated! :)

(It's totally ok that we have to manually update the version file for now.. probably the best thing that can be done for now :))

[sampajano]

Thanks so much again! LGTM just a few tiny nits and good to merge! :D

[meling]

Note: I added "versioned" comments also for PrintMethodDescriptorFile and PrintGrpcWebClosureES6File for consistency.

PS: Feel free to squash the commits into one for the merge.

[sampajano]

Thanks so much for your contribution and your patience on the comments! Much appreciated! :)

[sampajano]

BTW i've build a few binaries (for all 3 platforms) here:
https://github.com/grpc/grpc-web/actions

In case anyone is interested in downloading them :)