DEV: Absorb onebox gem into core (#12979)

* Move onebox gem in core library

* Update template file path

* Remove warning for onebox gem caching

* Remove onebox version file

* Remove onebox gem

* Add sanitize gem

* Require onebox library in lazy-yt plugin

* Remove onebox web specific code

This code was used in standalone onebox Sinatra application

* Merge Discourse specific AllowlistedGenericOnebox engine in core

* Fix onebox engine filenames to match class name casing

* Move onebox specs from gem into core

* DEV: Rename `response` helper to `onebox_response`

Fixes a naming collision.

* Require rails_helper

* Don't use `before/after(:all)`

* Whitespace

* Remove fakeweb

* Remove poor unit tests

* DEV: Re-add fakeweb, plugins are using it

* Move onebox helpers

* Stub Instagram API

* FIX: Follow additional redirect status codes (#476)

Don’t throw errors if we encounter 303, 307 or 308 HTTP status codes in responses

* Remove an empty file

* DEV: Update the license file

Using the copy from https://choosealicense.com/licenses/gpl-2.0/#

Hopefully this will enable GitHub to show the license UI?

* DEV: Update embedded copyrights

* DEV: Add Onebox copyright notice

* DEV: Add MIT license, convert COPYRIGHT.txt to md

* DEV: Remove an incorrect copyright claim

Co-authored-by: Jarek Radosz <jradosz@gmail.com>
Co-authored-by: jbrw <jamie@goatforce5.org>

spec/lib/onebox/engine/github_pullrequest_onebox_spec.rb

@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+describe Onebox::Engine::GithubPullRequestOnebox do
+  before do
+    @link = "https://github.com/discourse/discourse/pull/1253/"
+    @uri = "https://api.github.com/repos/discourse/discourse/pulls/1253"
+
+    stub_request(:get, @uri).to_return(status: 200, body: onebox_response(described_class.onebox_name))
+  end
+
+  include_context "engines"
+  it_behaves_like "an engine"
+
+  describe "#to_html" do
+    it "includes pull request author" do
+      expect(html).to include("jamesaanderson")
+    end
+
+    it "includes repository name" do
+      expect(html).to include("discourse")
+    end
+
+    it "includes commit author gravatar" do
+      expect(html).to include("b3e9977094ce189bbb493cf7f9adea21")
+    end
+
+    it "includes commit time and date" do
+      expect(html).to include("02:05AM - 26 Jul 13")
+    end
+
+    it "includes number of commits" do
+      expect(html).to include("1")
+    end
+
+    it "includes number of files changed" do
+      expect(html).to include("4")
+    end
+
+    it "includes number of additions" do
+      expect(html).to include("19")
+    end
+
+    it "includes number of deletions" do
+      expect(html).to include("1")
+    end
+
+    it "includes the body" do
+      expect(html).to include("http://meta.discourse.org/t/audio-html5-tag/8168")
+    end
+  end
+end