Explore: implement a basic autoloader

[daledupreez]

Fixes STRIPE-<linear_issue_id>
Fixes #<github_issue_id>

Changes proposed in this Pull Request:

This PR explores adding a basic autoloader for the plugin largely as a way to avoid unnecessary file loads across the plugin. I considered using some prefix matching before building the classmaps, but I decided against it as the overhead for building the classmaps is one-time, whereas performing multiple string prefix checks for every class we hit (including other classes) feels like it would quickly add up.

Another small change I included in this PR is to remove class instantiation side-effects from the class files so the effect is clearer from outside the class. I made changes so we're now auto-loading all classes, and I've moved the code that instantiated the classes from the respective class files to the main plugin file.

Testing instructions

There should be no change in behaviour as a result of this PR, as we're simply changing how we load the files containing the classes. Our unit tests and e2e tests should give us a basic safety net for the core autoloader functions, but it's possible that some edge cases exist.

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• Covered with tests (or have a good reason not to test in description ☝️)
• [N/A] Tested on mobile (or does not apply)

Changelog entry

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Changelog Entry Comment

Comment

Post merge

• Added testing instructions to the Release Testing Instructions wiki page (or does not apply)
• Added the needs docs label (or does not apply)
• Included this PR in the Release Thread scope (or does not apply)

[github-actions]

📈 PHP Unit Code Coverage Report

Package	Line Rate	Health
includes/abstracts/abstract-wc-stripe-payment-gateway.php	48%	❌
includes/admin/class-wc-stripe-inbox-notes.php	28%	❌
includes/class-wc-gateway-stripe.php	28%	❌
includes/class-wc-stripe-autoloader.php	6%	❌
includes/class-wc-stripe-customer.php	40%	❌
includes/class-wc-stripe-helper.php	59%	❌
includes/compat/trait-wc-stripe-subscriptions.php	20%	❌
includes/payment-methods/class-wc-stripe-express-checkout-helper.php	21%	❌
includes/payment-methods/class-wc-stripe-upe-payment-gateway.php	49%	❌
woocommerce-gateway-stripe.php	30%	❌
Summary	44% (7274 / 16420)	❌

[malithsen]

Looks great, thanks for pulling this together! The new autoloader cleans up our bootstrap nicely and should shave off unnecessary file loads. In the future, maybe we can explore moving to Composer with PSR-4 to get automatic class mapping and caching out of the box, it might require a large effort to restructure/rename our classes though.

[malithsen]

I was about to suggest adding a check to see if the file exists, to avoid fatal errors when there is a mapping to a non-existent file. However, I suppose throwing a fatal error is clearer than logging an error, which could be overlooked.