Some other widget packages use private classes for widgets - this fixes that

[nicko170]

Packages such as filament-apexcharts use private functions for getHeading() etc, which means this doesn't work.

This fixes that.

[what-the-diff]

PR Summary

• Improved Code Functionality
  The changes in the code on line 284 of the FilamentShield.php file are aimed at enhancing our feature's efficiency. Previously, we were directly accessing the $widgetInstance which didn't yield the desired results consistently. Now, the invade function is being used, which allows us to retrieve the header information from $widgetInstance. This results in increased accuracy and reliability of our software.

[bezhanSalleh]

Thanks!