Improve documentation for package_manager_bypass test module

📌 package_manager_bypass should *minimally* bypass php-tuf/composer-stager, not maximally Fixed landed, this is unblocked.

📌 Explore simplifying our fixture manipulation classes Fixed simplified this further (after 📌 package_manager_bypass should *minimally* bypass php-tuf/composer-stager, not maximally Fixed ), by adding a fixture_manipulator module.

So at this point I think the package_manager_bypass module has been sufficiently simplified that improving its documentation is now very simple.

This:

1. provides an accurate summary of what this module does right in the module description
2. renames services to clarify what they actually do
3. marks everything final and @internal
4. gets rid of the base class which was in its name tied to the stager, and turns it into a trait instead

this is so much better. Thanks @Wim Leers!

+++ b/package_manager/tests/modules/package_manager_bypass/src/PackageManagerBypassServiceProvider.php
@@ -21,12 +23,13 @@ class PackageManagerBypassServiceProvider extends ServiceProviderBase {
+    // By default, \Drupal\package_manager_bypass\Stager

I did forget to finish my thought here though 😅

By writing this comment, I realized package_manager_bypass' Stager, Beginner and Committer all ought to be named differently. So I did.

Finishing the thought…

Note that this commit broke Project Browser. Several classes used by PB were renamed here and made internal. @tedbow said it wouldn't be reverted, so we're adjusting here: 🐛 Fix tests after breaking change in Automatic Updates Fixed

Automatically closed - issue fixed for 2 weeks with no activity.