added getGuiItem method

[Lory9098]

No description provided.

[stefvanschie]

Thank you for your pull request. While I think a getGuiItem method can be useful, I don't quite agree with the approach taken here.

First, I don't think getGuiItem should be an abstract method in the Pane class. This method doesn't make sense for all panes, as demonstrated by PaginatedPane and MasonryPane that currently throw exceptions. Furthermore, it'd also mean components need to implement this method which is probably unnecessary and raises some questions about the exact implementation. For that reason, I think this method should be implemented only in the OutlinePane, StaticPane, and PatternPane classes.

Secondly, the method should take a Slot parameter, rather than an int so users can specify slots in their preferred way (either via a pair of coordinates or an index). Additionally, the return value is better represented as a regular GuiItem marked as @Nullable, without the Optional. The rest of the codebase doesn't use Optionals anywhere and instead uses annotations to mark whether results can be null. It is better to keep this consistent.

Additionally, some of the implementations appear to not work correctly. While the items in panes are often stored internally as a List, this does not necessarily mean the items are rendered linearly. Panes such as OutlinePane can render the items differently based on gaps, alignment, orientation, etc. PatternPane places items depending on the pattern specified. From a brief look, it seems to me only the implementation of StaticPane is correct currently.

Lastly, it seems that you have accidentally deleted the CI/CD. Please revert that, otherwise it'll be hard to merge your PR without causing interruptions.

If you can address these points, I'd be happy to merge your PR.