Fix dynamic properties and png rendering deprecations

[Vireth4114]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

• It fixes # (issue number, if applicable)
  closes Fixes deprecated dynamic property in baseclass.class.php and helpdeskplus.class.php #273 (most of the deprecated fields were fixed beforehand, but close_date, slaok and slako weren't).
• Here is a brief description of what this PR does
  • Fixes a few dynamic property deprecation
  • Fixes strftime deprecations
  • Fixes png related deprecations (most are float to int implicit conversion that was deprecated in php 8.1, and a removed argument in imagefilledpolygon() )

[trasher]

LGTM, appart my comment.

[Vireth4114]

I switched the displayed date in notification target to an IntlDateFormatter to accommodate localization. (And I also used the locale's "from %s to %s" instead of raw "du/au")