Add a selected_layers() function and refactor code to use it

[Keavon]

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[Keavon]

I believe we also wanted, in this PR, to change selected_layers_sorted to not create a new Vec. @TrueDoctor

[TrueDoctor]

I believe we also wanted, in this PR, to change selected_layers_sorted to not create a new Vec. @TrueDoctor

We actually can't because, as the name suggests, we need to sort the layers which is not possible without collecting them first

[AyeTbk]

Should this method (selected_layers) be in document_file.rs, on the Document type, instead of in document_message_handler.rs? To render the selection's bounding box in #282, the selected layers are needed (I currently compute them on my own, but I would like to reuse a prexisting method, if there is one). It also makes more sense to me for the Document to tell us what its selected layers are, instead of having code external to it having to toy with its innards to determine them...
(this goes for a lot of the methods in document_message_handler, I guess)

[TrueDoctor]

That sounds like a good idea

[Keavon]

That sounds like a good idea

@TrueDoctor Is that a change you could make then merge this? I only just realized we hadn't merged this yet. I am not sure I understand exactly what change to make per AyeTbk's suggestions.

[TrueDoctor]

That sounds like a good idea

@TrueDoctor Is that a change you could make then merge this? I only just realized we hadn't merged this yet. I am not sure I understand exactly what change to make per AyeTbk's suggestions.

Oh lol, I tought rhis code had already been merged xD

[TrueDoctor]

I dont think this pr is conceptually the right place to make that change.
The pr does what it says on the label and that is a good thing

[TrueDoctor]

Should this method (selected_layers) be in document_file.rs, on the Document type, instead of in document_message_handler.rs? To render the selection's bounding box in #282, the selected layers are needed (I currently compute them on my own, but I would like to reuse a prexisting method, if there is one). It also makes more sense to me for the Document to tell us what its selected layers are, instead of having code external to it having to toy with its innards to determine them...
(this goes for a lot of the methods in document_message_handler, I guess)

I think we should do a seperate pr in which we move lines 131-202 into the document_file but it makes sense to move them as a bunch

[TrueDoctor]

I will address the movement to the document file + further refactoring in the upcoming transforms api