Use uuid as GUID for Drupal entities

Getting php 8.1+ deprecation warning with the above patch

Deprecated function: trim(): Passing null to parameter #1 ($string) of type string is deprecated in Drupal\feeds\Feeds\Target\Uuid->prepareValue() (line 57 of /app/web/modules/contrib/feeds/src/Feeds/Target/Uuid.php)

Fixing php 8.1 deprecation warnings

Added an MR of the patch in #21 to make this easier to review and keep up to date.

I rewrote some of the comments for clarity, but the code looks good to me. All tests are passing, and I've been using this to import entities while specifying the UUIDs on a site for about a year now.

Although I created the MR, I did not write the original code (the MR was derived from patch #21), so I am setting this to RTBC based on my review and testing.

I merged the changes! Thanks all for contributing!

Automatically closed - issue fixed for 2 weeks with no activity.