* Update ringbuffer submodule to fix includes
* Remove cyclic includes
* Remove Qt include prefixes
* Include C++ versions of C headers
E.g.: assert.h -> cassert
* Move CLIP_BORDER_WIDTH into ClipView
This allows to remove includes to TrackView.h in ClipView cpp files.
* Elliminate useless includes
This improves the include structure by elliminating includes that are
not used. Most of this was done by using `include-what-you-use` with
`CMAKE_C_INCLUDE_WHAT_YOU_USE` and `CMAKE_CXX_INCLUDE_WHAT_YOU_USE`
set to (broken down here):
```
include-what-you-use;
-Xiwyu;--mapping_file=/usr/share/include-what-you-use/qt5_11.imp;
-Xiwyu;--keep=*/xmmintrin.h;
-Xiwyu;--keep=*/lmmsconfig.h;
-Xiwyu;--keep=*/weak_libjack.h;
-Xiwyu;--keep=*/sys/*;
-Xiwyu;--keep=*/debug.h;
-Xiwyu;--keep=*/SDL/*;
-Xiwyu;--keep=*/alsa/*;
-Xiwyu;--keep=*/FL/x.h;
-Xiwyu;--keep=*/MidiApple.h;
-Xiwyu;--keep=*/MidiWinMM.h;
-Xiwyu;--keep=*/AudioSoundIo.h
```
* Fixup: Remove empty #if-#ifdef pairs
* Remove LMMS_HAVE_STD(LIB|INT)_H
* Fix for Icons and comboboxes mismatch in arpeggiator in Instrument Editor #5494
(https://github.com/LMMS/lmms/issues/5494)
Introduce a static const int variable for the default height of a ComboBox.
Set this height already in the constructor of the ComboBox object.
Update all modules setting the height of a ComboBox object to make use of the new constant.
* Replace 'const int' by 'constexpr int' after review.
* advanced config: expose hidden constants to user screen
* advanced config: add support for FFT window overlapping
* waterfall: display at native resolution on high-DPI screens
* waterfall: add cursor and improve label density
* FFT: fix normalization so that 0 dBFS matches full-scale sinewave
* FFT: decouple data acquisition from processing and display
* FFT: separate lock for reallocation (to avoid some needless waiting)
* moved ranges and other constants to a separate file
* debug: better performance measurements
* minor fixes
* build the ringbuffer library as part of LMMS core
