* [PHP] - Add FormDataProcessor to handle nested ModelInterface data
* Generating samples
* Updates php-nextgen and psr-18
* Adds tests
* Some more tests
* One last test
* Updating files
* Fixing diff
* Test fix
* Updating samples
* Output of CLI commands per PR comments
* Rebuilding PHP examples, PSR-18
* Rebuilding PHP examples
* Adds explanation for ::flatten_array(); optimized array_is_list pollyfill
* [PHP] Fix converting objects to formdata
* flatten_array -> flattenArray to match code style
* Adds unit test
* Revert "Output of CLI commands per PR comments"
This reverts commit 2eaa93731c.
* Includes php-nextgen; tightens up ::toFormValue()
* Missing ArrayAccess import
* Adds test for refactored ObjectSerializer::toFormValue()
