Make all php classes strict

[ChristophWurst]

Description

If you look at code like https://github.com/nextcloud/server/blob/master/apps/dav/lib/DAV/CustomPropertiesBackend.php then you see that not all of our php code has declare(strict_types=1); yet.

It's time to clean this up, force PHP into strict mode and out of unpredictable type juggling. This might cause some errors, but they are valid and should be fixed.

Affected components

• CalDAV and CardDAV backends
• Calendar
• Calendar Resource Management
• Contacts
• Contacts Interaction
• Mail

To do

Search each app for those files (bash search magic?) and fix them. If the number of files touched is large, break the PRs done into one PR per namespace.

• CalDAV and CardDAV backends
  • Make all CalDAV PHP classes strict server#30437
• Calendar
• Calendar Resource Management
• Contacts
• Contacts Interaction
• Mail