PHP Tests: More robustness, PluginFactory, improved Multisite handling

[swissspidy]

Context

• Add randomly-ordered unit test run to GHA workflow ampproject/amp-toolbox-php#328
• PHP Tests: More robustness, PluginFactory, improved Multisite handling #8792 (comment)
• Add hooks for create and delete sites. #7494

Summary

This PR adds a single PHPUnit run that is randomly ordered.

This can detect scenarios where the test makes assumptions that are only fulfilled by global state manipulated by a previous test, but are not true in the actual logic to be tested.

In case such a randomly ordered test run fails, the random seed can be found in the GHA log so that this particular ordering can be replicated locally.

Relevant Technical Choices

Add a randomly ordered test run to the GHA workflow

Adds a single PHPUnit run that is randomly ordered.

This can detect scenarios where the test makes assumptions that are only fulfilled by global state manipulated by a previous test, but are not true in the actual logic to be tested.

In case such a randomly ordered test run fails, the random seed can be found in the GHA log so that this particular ordering can be replicated locally.

Note: This PR also fixes some tests that failed during these randomly ordered test runs, but not all. There are simply too many issues with the tests, which requires another big overhaul.

Adds new HasSiteSetup and HasSiteRemoval interfaces

Eliminates the procedural setup_new_site() code by moving logic attached to site setup/teardown in Multisite to the individual services. Basically implementing #7494

Added bonus: rewrite rules are no longer flushed twice upon plugin activation (once by the service container and once by setup_new_site().

Renames existing similar interfaces accordingly:

• PluginActivationAware
• PluginDeactivationAware

PluginFactory

Replaces get_plugin_instance() with a dedicated PluginFactory and a simple bootstrap_plugin() function which is hooked to plugins_loaded.

Before that, the plugin was executed right away and not attached to any particular action.

Link_Controller / Hotlink_Controller

Fixes a bug in Link_Controller which unexpectedly caused an external HTTP request.

Slightly refactored both classes to be more aligned and use wp_http_validate_url() for URL validation.

Updates tests accordingly.

To-do

• Split up integration tests and unit tests (PHP Tests: Separating unit and integration tests #5473)
• Make use of DependencyInjectedTestCase
• Fix all the issues with the tests ⚠️

User-facing changes

N/A

Testing Instructions

• This is a non-user-facing change and requires no QA

Reviews

Does this PR have a security-related impact?

Does this PR change what data or activity we track or use?

Does this PR have a legal-related impact?

Checklist

• This PR addresses an existing issue and I have linked this PR to it in ZenHub
• I have tested this code to the best of my abilities
• I have verified accessibility to the best of my abilities (docs)
• I have verified i18n and l10n (translation, right-to-left layout) to the best of my abilities
• This code is covered by automated tests (unit, integration, and/or e2e) to verify it works as intended (docs)
• I have added documentation where necessary
• I have added a matching Type: XYZ label to the PR

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Fixes #

[spacedmonkey]

This is the last thing - #8792 (comment) then I will approve.

[spacedmonkey]

👍