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>

lib/onebox/engine/pastebin_onebox.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+module Onebox
+  module Engine
+    class PastebinOnebox
+      include Engine
+      include LayoutSupport
+
+      MAX_LINES = 10
+
+      matches_regexp(/^http?:\/\/pastebin\.com/)
+
+      private
+
+      def data
+        @data ||= {
+          title: 'pastebin.com',
+          link: link,
+          content: content,
+          truncated?: truncated?
+        }
+      end
+
+      def content
+        lines.take(MAX_LINES).join("\n")
+      end
+
+      def truncated?
+        lines.size > MAX_LINES
+      end
+
+      def lines
+        return @lines if defined?(@lines)
+        response = Onebox::Helpers.fetch_response("http://pastebin.com/raw/#{paste_key}", redirect_limit: 1) rescue ""
+        @lines = response.split("\n")
+      end
+
+      def paste_key
+        regex = case uri
+                when /\/raw\//
+                  /\/raw\/([^\/]+)/
+                when /\/download\//
+                  /\/download\/([^\/]+)/
+                when /\/embed\//
+                  /\/embed\/([^\/]+)/
+        else
+                  /\/([^\/]+)/
+        end
+
+        match = uri.path.match(regex)
+        match[1] if match && match[1]
+      end
+    end
+  end
+end