This reverts commit 42a2f19.

…ment-qt6

This reverts commit 9470abc, reversing
changes made to c77b93b.

This reverts commit 09de46e.

This reverts commit 5bd8290.

The following changes are applied to make the minimum build configuration compile:
*  Remove usage of a `QKeyEvent` constructor in `ColorChooser.h` by directly forwarding the original event.
* Change `QMap` to `QMulitMap` in several places in `ControlLayout.h` because that's what in fact is used.
* Change the parameter from `QEvent` to `QEnterEvent` in some `enterEvent` overrides.
* Add an include for `algorithm` in `MixHelpers.cpp`
* Fix a problem with string argument replacement in `embed.cpp`
* Introduce the usage of `QKeySequence` including the replacement of the `+` operator with the `|` operator.
* Add an include for `QActionGroup` in `ProjectNotes.cpp`.
* Use `QPalette::window` instead of `QPalette::background` in `ClipView.cpp`
* Use `qBound<panning_t>` instead of `qBound<int>` in `PianoRoll.cpp`. Add a cast.
* Replace the deprecated call to `QLayout::setMargin` with `QLayout::setContentsMargins`

Note: there are still lots of warnings when you compile this state with Qt6!

Fix the Qt5 build for `ControlLayout` by intoducing typedefs depending on the Qt version and using these throughout `ControlLayout`.

Use `setContentsMargins` instead of `setMargin`.

Add the dependency to "Core5Compat" to the main CMakeLists.txt. It is needed so that we can use `QTextCodec` which is used by the Hydrogen importer plugin.

Adjust the CMakeLists.txt of the ZynAddSubFx plugin so that it also makes use of `QT_VERSION_MAJOR` and therefore builds under Qt5 and Qt6.

Fix the build that failed after the merge of master. The data type that `QColor::getRgbF` uses has changed between Qt5 and Qt6. This is solved with a using because changing the type to `float` which is used by Qt6 did not work with Qt5 either.

Fix warnings in `AutomationClip.cpp`. These have been warnings of the type:
"Warning: »QMap<int, lmms::AutomationNode>::const_iterator operator-(QMap<int, lmms::AutomationNode>::const_iterator, QMap<int, lmms::AutomationNode>::const_iterator::difference_type)« is deprecated: Use std::prev; QMap iterators are not random access [-Wdeprecated-declarations]

Fix build warning about deprecated iterator operators in `AutomationClipView`.

Fix the deprecated usage of the following methods:
* `QMouseEvent:x()`
* `QMouseEvent:y()`
* `QDropEvent:x()`
* `QDropEvent:y()`

This is done by adding two new helper methods names `position` to `DeprecationHelper.h` and using these methods in the event methods.

Fix more warnings about iterator operators by using `std::prev` and `std::next`.

Fix warnings about `QKeyCombination::operator+`.

Co-authored-by: Dalton Messmer <messmer.dalton@gmail.com>