Fix: update REST API v3 reports/orders/totals endpoint to be compatible with HPOS

[lsinger]

Submission Review Guidelines:

• I have followed the WooCommerce Contributing Guidelines and the WordPress Coding Standards.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• I have reviewed my code for security best practices.
• Following the above guidelines will result in quick merges and clear and detailed feedback when appropriate.

Changes proposed in this Pull Request:

This PR updates the REST API v3 reports/orders/totals endpoint to be compatible with HPOS.

Closes woocommerce/woocommerce-ios#12468.

How to test the changes in this Pull Request:

Using the WooCommerce Testing Instructions Guide, include your detailed testing instructions:

1. checkout the branch locally and then move HEAD to the first commit that adds the failing test
2. run the test, observe that it fails: pnpm test:php:env --filter=WC_Tests_API_Reports_Orders_Totals
3. move HEAD to the tip of this branch again
4. run the test, observe that it passes: pnpm test:php:env --filter=WC_Tests_API_Reports_Orders_Totals
5. ensure CI checks pass

Changelog entry

• Automatically create a changelog entry from the details below.

Significance

• Patch
• Minor
• Major

Type

• Fix - Fixes an existing bug
• Add - Adds functionality
• Update - Update existing functionality
• Dev - Development related task
• Tweak - A minor adjustment to the codebase
• Performance - Address performance issues
• Enhancement - Improvement to existing functionality

Message

Comment

[github-actions]

Hi @jorgeatorres,

Apart from reviewing the code changes, please make sure to review the testing instructions as well.

You can follow this guide to find out what good testing instructions should look like:
https://github.com/woocommerce/woocommerce/wiki/Writing-high-quality-testing-instructions

[jorgeatorres]

Just for completeness, some instructions to test outside of the test suite:

1. Select "WordPress post storage" as datastore in WC > Settings > Advanced > Features. Compatibility mode should be disabled.
2. Populate the site with some orders (i.e. via wp wc generate orders).
3. Use the API client of your choice to make a GET request to https://<yoursite>/wp-json/wc/v3/reports/orders/totals.
4. Take note of the results.
5. Run wp cot sync to sync orders to HPOS.
6. Select "High-performance order storage" as datastore in WC > Settings > Advanced > Features. Keep compatibility mode disabled.
7. Repeat step 3 and confirm the results are identical to those from step 4.

[jorgeatorres]

LGTM. Works as described. Thank you @lsinger!