Stay-on-top prevents floating windows to get focus

[musikBear]

Related to #6115

When "stay on top" on an instrument window is used it will create artefacts on larger windows and also prevent floating windows to gain focus

Steps to reproduce

Bug with floating windows
In order to have several windows for testing, open an example project.

• Pick any instrument and place it anywhere over song-editor.
• Use stay on top for the instrument
• Open Piano-roll as a floating window
  We now have this:
  
  Click anywhere on the piano-roll -f.i. in the yellow marking.
  Piano-roll 'disappear' or is rather sent to the back of the windows, including song-editor, so it seams to disappear.
  If Stay on top is disabled on the instrument, it is again possible to work in piano-roll
  Random occurring Bug with non-floating windows
  This happens unpredictable and is not reproduceable
  If Stay on top** is activated on an instrument it is not possible to open any other full-screen window on top of the stack.
  Clicking the toggle-button or using hot-key for any window will open that window on the bottom of the stack and below song-editor

Expected behavior

Stay on top** instrument should overlap piano-roll

Actual behavior

Stay on top** instrument should not have the result that piano-roll window is sent to the bottom of the stack of floating windows, if it is clicked

Affected LMMS versions

windows 1.21, 1.22 & 1.3 Alpha

It is strange that this has not been reported before. It makes me believe that no one is using Stay on top

[Manerr]

I've exactly the same issue on 1.3.0 alpha (I thought it was a normal behaviour) -> In my mind I was thinking: since it's on top it was just taking a focus priority ( + the display priority of course)