Fix: Form Builder: Subscribe and store entry when Name field removed

[n7studios]

Summary

Fixes a PHP notice, and the form entry not being stored correctly, when the Name field is removed from a Form Builder block.

maybe_subscribe() read $form_data['first_name'] directly when storing form entries. If the Name field was removed from the block, first_name isn't submitted, resulting in an Undefined array key "first_name" PHP notice for each entry stored.

The first name is now read once, falling back to a blank string if the Name field isn't included, and used when creating the subscriber and storing entries.

Testing

New Integration test in BlockFormBuilderTest:

• testSubscribeWhenNameFieldRemoved: submits the block without a first name, and confirms the subscriber is created without a first name and the entry is stored. Fails without this fix.

BlockFormBuilderTest::submit() now accepts an include_name parameter, to submit the block without the Name field.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)