Explicitly load the sqlite-database-integration/php-polyfills.php file

[fredrikekelund]

Fixes https://github.com/Automattic/dotcom-forge/issues/10054

In https://github.com/Automattic/dotcom-forge/issues/10054, we discovered that exports are currently broken in Studio when running PHP <8. This happens because str_ends_with is used in the sqlite-database-integration codebase, but that function only became part of PHP's stdlib in version 8. The crux is that sqlite-database-integration actually has a polyfill for this function, but that polyfill isn't loaded. This happens because we use the before_wp_load hook for the WP-CLI commands in this project, short-circuiting WP's regular logic for loading mu-plugins. Instead, we manually require files from sqlite-database-integration, but we hadn't previously included php-polyfills.php. This PR fixes that.

Testing instructions

1. Clone this PR locally
2. Run composer install --no-dev --optimize-autoloader --ignore-platform-reqs in this repo
3. Replace wp-files/sqlite-command in the Studio repo with a symlink to your local wp-cli-sqlite-command repo
4. Apply 3658f-pb to the Studio repo
5. Run npm start
6. In the Settings tab, change the PHP version to 7.4
7. In the Import/Export tab, click "Export database"
8. Ensure a SQL dump is created successfully

[wojtekn]

@fredrikekelund, the fix by loading polyfills explicitly looks valid, and it fixes the issue for me.

Are src/SQLite_Command.php changes leftovers from the previous implementation that should be removed?

[fredrikekelund]

I realized the SQLiteDatabaseIntegrationLoader::load_plugin() method already performs an equivalent check. No need to duplicate that logic.

[fredrikekelund]

After discussing the initial changes in this PR with @wojtekn, we concluded that this method could also be static, and there's really no reason for the command classes to extend this class. Hence, I took the opportunity to make this into a standalone class with only static methods.

[wojtekn]

Works as expected. Thanks for the cleanup!