Fix bottom dock offsets and change Audio to EditorDock

[KoBeWi]

Part of #113024
Fixes #112616

The way #111499 was implemented is not compatible with the new bottom panel. Not all bottom docks are children of the bottom panel, and also EditorDocks are not being added to bottom_docks list, so the code required some changes. The offsets are now stored in a Dictionary, so layout saving is no longer dependent on what dock happens to be at the bottom.

#112616 is fixed by adding a default Audio size to the default layout and loading it on initial launch (similar to #113232 in its original form).

[lodetrick]

I'm getting this error when starting up the editor:

ERROR: Couldn't find the given section "EditorNode" and key "bottom_panel_offsets", and no default was given.

I don't know if it was related but the audio offset was not updated either (even when loading from default)

[KoBeWi]

The default Audio size is loaded only when initializing editor layout for the first time (i.e. the file was never saved in the project or was deleted).

[arkology]

i.e. the file was never saved in the project or was deleted

What about not saving audio tab offset if its offset is 0? I think in this case "default" value will be loaded every time, right?

[KoBeWi]

No

[Calinou]

Tested locally, it works as expected. Code looks good to me.

The dock can't be moved to the side by design, but you can turn it into a floating window, which is useful to make it taller:

[Repiteo]

Thanks!

[arkology]

Tested locally, it works as expected. Code looks good to me.

The dock can't be moved to the side by design, but you can turn it into a floating window, which is useful to make it taller:

If we talk about its size, then it can still be fitted into editor sides with some changes. The minimum width is limited by the top panel of this dock, and after reducing it (for quick testing, I just removed the text from all the buttons), the panel fits pretty well into the side panels.