Standardize Plugins Layouts

[JohannesLorenz]

Enhancement Summary

Currently, our Lv2 and LADSPA designs differ a lot (feel free to fix/update this table):

	CLAP	LADSPA	Lv2	VST	VST3	Suggestion
Linkable Models?	No	Yes	No (surprising)	?	No	No (#7201)
HiDPI redesigned controls	No	Yes	No	?	No	Yes (#6798)
Checkbox for booleans	Yes	No	Yes	No	Yes	Yes?
Spinbox for integers	Yes	No	Yes	No	Yes	Yes?
Code base for Layout	ControlLayout	"LADSPA"	ControlLayout	"VST"	ControlLayout	Common?

Relevant PRs/Issues:

• #6456
• #6798
• #2068
• #7201

Involved Developers:

• @michaelgregorius (HiDPI redesigned controls)
• @DomClark (VST3, #6456)
• @zonkmachine (#6798)
• @JohannesLorenz (Lv2)
• @messmerd (CLAP)

Implementation Details / Mockup

The implementation depends on whether we want to spend time making LADSPA, Lv2 and VST and VST3 share the same Layout.

• If yes, we would only need to fix it in one layout, e.g. ControlLayout
• If not, there will be a lot of different subtasks (like "Let Lv2 use HiDPI controls", "remove linkable models from LADSPA" etc)

Please search the issue tracker for existing feature requests before submitting your own.

• [X] I have searched all existing issues and confirmed that this is not a duplicate.