fix: update PageBuilder for Filament v4 compatibility

[mckenziearts]

This PR updates the PageBuilder component to be compatible with Filament v4.

Change

Action Mounting

• Replaced mountFormComponentAction() with mountAction() which is the correct method in Filament v4
• Added proper action context using { schemaComponent: '{$key}' } instead of passing the statePath as the first argument
• Added $key = $getKey() in the main page-builder template to provide the component key
• Passed :key="$key" prop to all block picker components (dropdown and modal variants)

Component Updates

• Replaced x-filament::grid component with plain div using Tailwind classes (grid gap-1) in dropdown-block-picker
• Changed if ($afterItem) to if (filled($afterItem)) for consistency with Filament conventions

Breaking Changes

None - this maintains backward compatibility while adding v4 support.

Additional Context

In Filament v4, the action mounting system changed from mountFormComponentAction(statePath, actionName, arguments) to mountAction(actionName, arguments, context) where context is an object containing schemaComponent key. This PR updates all block picker components to use the new API.

[what-the-diff]

PR Summary

• Updated Namespace Import for Action
  Changed the location from where the Action class is being imported in a necessary file which should lead to better organization of the code.

• Added consistent unique key handling
  By introducing a $key variable, we make sure unique keys are passed consistently. This should enhance stability and predictability in related functions.

• Improved Component Attributes
  Multiple component attributes were updated to acknowledge the new :key="$key" attribute. Greater accuracy and control are expected with this update.

• Modified Parameter Arrays
  By adding 'key' to the parameter arrays, it becomes easier to reference this important parameter further in the code.

• Refined Value Checking
  Updated the method for checking if values exist, aiming for a more robust and error-free result.

• Refactored Action Mounting
  Switched to a more efficient method to mount actions, which also includes the new key. This should boost the performance of related processes in the system.

• HTML Structure Adjustment
  Changed the HTML structure in one of the files for increased flexibility, which should lead to better adaptability for various screen sizes and devices.

• Class Name Adjustments
  Minor changes to the class names for buttons and icons were made which should improve consistency in the visual design.

[Voltra]

If the component is still available, I think it's best we keep it until it's deprecated

[Voltra]

What about x-filament-schemas::grid?

[mckenziearts]

This component no longer exists on filament v4 you must use a div instead.

[Voltra]

LGTM

can always change back the grid component if needed

[Voltra]

@Z3d0X ready for a release