Refactor installer class to load dependencies when needed

[mikkamp]

Changes proposed in this Pull Request:

This PR makes 2 main refactors to the Installer class.

1. Remove validation

In the constructor we were explicitly passing all classes which implement InstallableInterface and then validating to check if they implemented the same interface. Since the container is responsible for passing the right dependencies we don't need to do another loop through those classes to validate them.

2. Load dependencies when needed

Passing the dependencies in the constructor means it will call the constructor of all the dependencies, even when we don't use them. Since the Install class relies on a hook being called and some other additional conditions, we can retrieve the necessary classes from the container only when they are needed. This is a minor optimization in how the extension constructs itself, but together with other optimizations it will make a difference.

If we look at the before and after of a front end request we can see that it reduces the time spent resolving container dependencies.

Before:

After:

Since we changed the load order this was initially generating a fatal error:

PHP Fatal error:  Uncaught TypeError: Automattic\WooCommerce\GoogleListingsAndAds\Product\Attributes\AttributeManager::__construct(): Argument #1 ($attribute_mapping_rules_query) must be of type Automattic\WooCommerce\GoogleListingsAndAds\DB\Query\AttributeMappingRulesQuery, string given in google-listings-and-ads/src/Product/Attributes/AttributeManager.php:69

This was because the DBServiceProvider wasn't registered as the provider of this class, so it wasn't resolving when loading in a different order.

Detailed test instructions:

1. Use the snippet add_filter( 'woocommerce_gla_force_run_install', '__return_true' );
2. Remove the option gla_db_version
3. Remove the option gla_install_version
4. Refresh an admin page and confirm the options are re-added
5. Remove one of the DB tables like wp_gla_budget_recommendations
6. Refresh an admin page and confirm it's added again

Changelog entry

• Tweak - Refactor installer class to load dependencies when needed.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 67.1%. Comparing base (c8c1efa) to head (bd78fab).
Report is 7 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/Installer.php	0.0%	6 Missing ⚠️
...ernal/DependencyManagement/CoreServiceProvider.php	0.0%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             develop   #2764     +/-   ##
===========================================
+ Coverage       67.0%   67.1%   +0.1%     
+ Complexity      4692    4688      -4     
===========================================
  Files            480     480             
  Lines          19601   19583     -18     
===========================================
  Hits           13141   13141             
+ Misses          6460    6442     -18     

Flag	Coverage Δ
php-unit-tests	67.1% <0.0%> (+0.1%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...nternal/DependencyManagement/DBServiceProvider.php	6.2% <ø> (ø)
...ernal/DependencyManagement/CoreServiceProvider.php	0.0% <0.0%> (ø)
src/Installer.php	0.0% <0.0%> (ø)

[puntope]

LGTM ✅ Thanks for the refactor

THe options are recreated correctly:

I also tested Attribute Mapping feature and works as expected.

Notice it's not necessary to add the snippet. Because if we delete gla_db_version then the installer and first_installer will trigger as the first check is true https://github.com/woocommerce/google-listings-and-ads/pull/2764/files#diff-67306479da293f095927542c4cff1a45875138eb52372caaba982b07c053285bL82 .