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/widget/timelinewidget/tool/edit.cpp

@@ -21,6 +21,7 @@
 
 #include "edit.h"
 #include "widget/timelinewidget/timelinewidget.h"
+#include "widget/timelinewidget/trackhandle.h"
 
 namespace olive
 {
@@ -84,9 +85,10 @@ void EditTool::mouse_release(TimelineViewMouseEvent *event)
 
 void EditTool::mouse_double_click(TimelineViewMouseEvent *event)
 {
-	Block *item = parent()->get_item_at_scene_pos(event->get_coordinates());
+	OakEngineBlock *item =
+		parent()->get_item_at_scene_pos(event->get_coordinates());
 
-	if (item && !item->track()->is_locked()) {
+	if (item && !track_is_locked(oakengine_block_get_track(item))) {
 		parent()->add_selection(item);
 	}
 }