LV2 plugin layout

### Summary

Observations and suggestions for the LV2 instrument/effect plugin layout.

- [ ] (A) Help button takes up all of the top layout. There is all this space to the left of it. It could share space with the search field.
- [ ] (B) Checkboxes - Text size is too large. Pictures 2 and 3.
- [x] (C) Search field is visible on layouts with more than two items. I think that's too low. You don't need a search field for three items. I think it could be larger still. At least six. Picture 3. https://github.com/LMMS/lmms/blob/bc99728534c90fba25c5deedef1568dc5d9d6e62/src/gui/ControlLayout.cpp#L262
- [x] (D) There are LV2 plugins that have both portProperty **Toggled** and **Integer** (Example: [Redeye - Chump](https://github.com/brummer10/guitarix/blob/master/trunk/src/LV2/gx_redeye.lv2/gx_redeye.ttl#L102-L103)). Picture 1. These ports currently show up as LCD displays but on other DAW's they are presented as checkboxes and this seem to be the correct way. If I move the test for Toggled in the code below to the top, before Integer, the checkbox shows correctly. I don't know what else breaks but it's just a test. https://github.com/LMMS/lmms/blob/bc99728534c90fba25c5deedef1568dc5d9d6e62/src/core/lv2/Lv2Ports.cpp#L117-L123
- [ ] (E) ComboBox text width is too small. Pictures 4 and 5.

#### Screenshot

1 - master

2 - Test for toggle first

3 - Search field on > 6 items

4 - ComboBox text width, today 64

5 - ComboBox text width, increased to 96

Start with src/gui/ControlLayout.cpp and src/core/lv2/Lv2Ports.cpp, especially the layout threshold and port-property checks linked in the issue. Review the unchecked items for the help/search layout, checkbox sizing, and combo-box width. Done means the LV2 controls use the intended layout and toggled integer ports appear as checkboxes without regressions.

Written by the indexing model from the issue text.