R8: finish app/ pure C ABI migration (P3-P9) and make OTIO required

- app/ no longer includes engine C++ headers nor holds engine C++ types:
  engine access goes through the oakengine C ABI plus C++ wrappers
  (oakutil/oaknode.h, oakutil/oakvideo.h) and app-local mirror types
  (tooltypes, trackreferencehandle, timelinecommonapp, keyframetypes,
  subtitleapp, serializedlayoutinfoapp, nodevaluehandle, sliderdisplaytypeapp)
- engine: new C ABI functions for block/track/clip/transition navigation
  and predicates, links, caches, waveform/playback, disk folder,
  sequence_track_list, node_free, footage_is_valid, block_get_track,
  get_brush; loadotio/saveotio ported to the current engine API
- OTIO is now a required dependency: CI and CD build it on every
  platform, FindOpenTimelineIO fixed for OTIO 0.16/0.19 (the old deps
  include requirement silently disabled OTIO everywhere), runtime
  libraries are bundled into packages and copied next to macOS binaries
  (oak_copy_otio_runtime)
- fix ProjectViewModel drag&drop mime read/write size mismatch (segfault)
- unify color label naming (k_olive -> "Oak") in the app-side mirror
- docs: OTIO required, FFmpeg minimum corrected to 6.0 (en/zh)
- gtest suite: 1925 passed, 0 failed

app/panel/sequenceviewer/sequenceviewer.cpp

@@ -33,7 +33,7 @@ SequenceViewerPanel::SequenceViewerPanel()
 }
 
 void SequenceViewerPanel::start_capture(const TimeRange &time,
-									   const Track::Reference &track)
+										const TrackReference &track)
 {
 	TimelinePanel *tp = static_cast<TimelinePanel *>(sender());
 	static_cast<ViewerWidget *>(get_time_based_widget())

app/panel/sequenceviewer/sequenceviewer.h

@@ -22,6 +22,7 @@
 #ifndef OAK_SEQUENCEVIEWERPANEL_H
 #define OAK_SEQUENCEVIEWERPANEL_H
 
+#include "common/trackreferencehandle.h"
 #include "panel/viewer/viewer.h"
 
 namespace olive
@@ -33,7 +34,7 @@ public:
 	SequenceViewerPanel();
 
 public slots:
-	void start_capture(const TimeRange &time, const Track::Reference &track);
+	void start_capture(const TimeRange &time, const TrackReference &track);
 
 protected:
 	virtual void retranslate() override;