Gift Upgrades 2.5.2

• Confirm support for XenForo 2.3+.
• Bump minimum PHP version to 8.0+.
• Code cleanup.

• Fix the gift upgrades alert triggered by gifting a post would not link to the post.
• Fix compatibility issue with XF 2.2.15.

• Require Standard Library by Xon v1.18.0+
• Fix sending the user upgrade receipt to the receiving user instead of the paying user.
• Adjust the phrase in line item to list the sending and receiving user.
• Add option "Allow gifting on warned content" to control if users can gift to warned posts.
• Add option "Display gifting on warned content" to control if users can see if warned posts have a gift.
• Enable searching for posts/threads/profile posts which have had a gift given to them.

• Fix anonymous gifts not being marked as anonymous as expected.
• Fix "Cannot call method canGiftTo on a non-object (NULL)".
• Fix incorrect visibity on the _postDelete() method in the GiftUpgrade entity.
• Fix a potential issue where gifted upgrades were not marked as such.
• Add additional indexes to xf_user_upgrade_expired/xf_user_upgrade_active tables.

• Only inject User Essentials templates if that add-on is active.

• Add missing relation to UserUpgradeExpired entity.
• Fix issue with permission checking logic when verifying if a user can be content gifted.

• Allow recurring upgrades to be gifted. The first term will be paid for by the gifter and the giftee can choose to renew upon its expiration.
• Expose Recent Gift Post's widget date limit as a configurable option.
• Add missing relation to the UserUpgradeExpired entity.
• Fix potential issues surrounding the giving of free gifts.

• Add icon back to the "Gift" button.
• Allow sending free gifts from the account upgrades page.
• Fix a no permissions error that could occur when gifting from the account upgrades page.

• Allow users with permission to gift user upgrades for free.
• When fresh installing the add-on, ensure the registered group gets permissions to send gifts.
• Add a gift link to messages sent within Siropu's Chat add-on.
• Adjust permission checking when gifting content.
• Minor code clean up.

Includes changes from v2.3.0 because I forgot to post that, oops

• Add option "Exclude warned posts" from recent gifted posts.
• Add an icon to the "Gift" button.
• Fix MySQL 8.0 compatability when upgrading from versions earlier than 2.1.0.