[Lv2/SPA] Using instrument window arrow keys fails to resize

[JohannesLorenz]

When you use the arrow keys of the instrument track view (top right) to switch instruments, if the instruments have different sizes, sometimes the dialogue does not resize.

Reproduce on lv2-review (#4899):

• Open LMMS main window, do nothing else
• Drag the lv2-testsignal-generator on the instrument board
• Open the triple-oscillator instrument window
• Use an arrow to switch the window to use the lv2-testsignal-generator

The bug also occurs if you open the lv2-testsignal-generator first and then switch to 3osc. It does not always occur if you have had both instruments open without ever using the arrows. It's some strange caching behaviour, which may be fixed/removed in #3623 .

• Branches: all
• Observable on: Any with variable-sized instrument windows. At least lv2-review (Lv2 core implementation #4899) and soon on osc-plugin (Implement SPA support (enabling zyn-fusion) #4662) .
• Introduced: Merge of branch variable-tab-widget (Variable tab widget #4906) into master (not as a regression issue, but as a bug of the new feature).

[PhysSong]

Reproduced with LV2. I'll see if it's related to #3623.

[PhysSong]

Dropping the caching system seems to fix this issue. I left with re-implementing the One Instrument Track Window Mode feature now.

[JohannesLorenz]

No need to use the arrow keys. As @douglasdgi reported, you can

1. add tracks for triple-oscillator and lv2-testsignal-generator
2. open triple-oscillator's instrument window
3. close it
4. open lv2-testsignal-generator's instrument window

Then, the testsignal generator will have the same size as the 3osc (which is wrong). @PhysSong does your fix also fix this variant?

[PhysSong]

It looks like an almost identical issue, and the same patch should fix it. I haven't tested that yet, though.

[PhysSong]

Found a third variant:

1. Add a TripleOscillator.
2. Open it.
3. Drag and drop lv2-testsignal-generator to the open window.
4. Boom!

This variant is more complicated, but I found a fix which seems to work for all observed variants even without fixing the InstrumentTrackWindow caching problem.