style: unify identifier naming per updated conventions

Automated with clang-tidy readability-identifier-naming (config added to
.clang-tidy) plus scripted passes, per the updated rules now documented
in CONTRIBUTING.md:

- types (class/struct/enum/alias/template params): PascalCase
- functions, variables, members: snake_case (incl. rational -> Rational)
- private/protected members: trailing underscore; static member
  variables likewise (instance_, available_themes_)
- constants and enum values: snake_case (kLinear -> k_linear,
  F32P -> f32p); ALL_CAPS reserved for macros
- macros: OAK_ prefix (OLIVE_ADD_TEST/OLIVE_ASSERT/OLIVE_CONFIG ->
  OAK_ADD_TEST/OAK_ASSERT/OAK_CONFIG, GL_PREAMBLE -> OAK_GL_PREAMBLE,
  include guards -> OAK_*)
- file names: all lowercase (Current/Plugin/OliveHost/OliveClip/
  OlivePluginInstance -> current/plugin/olivehost/oliveclip/
  oliveplugininstance)
- getters share the member name sans underscore, setters set_foo()
- Qt and third-party (OpenFX) virtual overrides and framework callbacks
  keep their original names (exempt in .clang-tidy)

Manual follow-ups required where automation could not reach:
- string-based QMetaObject/SIGNAL/SLOT references updated to renamed
  methods (AddTask, CreatedFile, DeleteSpecificFile, moveSelectionUp, ...)
- macro bodies referencing renamed methods (OLIVE_CONFIG,
  NODE_DEFAULT_DESTRUCTOR, MANAGEDDISPLAYWIDGET_*)
- self-shadowing locals renamed where signals/methods became same-named
  (size_changed, worker_count, selected_items, import param, filters)
- third_party OFX member/namespace usages restored (OFX::Host::*,
  _created, _clipPrefsDirty, createInstance, clearPersistentMessage)
- STL protocol aliases restored (const_iterator) with .clang-tidy
  ignore rules; qHash overloads restored

Full build and test suite pass: ctest 4/4, ~1960 gtest cases green.

app/undo/undostack.cpp

@@ -26,7 +26,7 @@
 namespace olive
 {
 
-const int UndoStack::kMaxUndoCommands = 200;
+const int UndoStack::k_max_undo_commands = 200;
 
 class EmptyCommand : public UndoCommand {
 public:
@@ -34,7 +34,7 @@ public:
 	{
 	}
 
-	virtual Project *GetRelevantProject() const override
+	virtual Project *get_relevant_project() const override
 	{
 		return nullptr;
 	}
@@ -57,7 +57,7 @@ UndoStack::UndoStack()
 	connect(redo_action_, &QAction::triggered, this, &UndoStack::redo);
 
 	clear();
-	UpdateActions();
+	update_actions();
 }
 
 UndoStack::~UndoStack()
@@ -79,7 +79,7 @@ void UndoStack::push(UndoCommand *command, const QString &name)
 	// Clear any redoable commands
 	this->beginRemoveRows(QModelIndex(), commands_.size(),
 						  commands_.size() + undone_commands_.size());
-	if (CanRedo()) {
+	if (can_redo()) {
 		for (auto it = undone_commands_.cbegin(); it != undone_commands_.cend();
 			 it++) {
 			delete (*it).command;
@@ -95,14 +95,14 @@ void UndoStack::push(UndoCommand *command, const QString &name)
 	this->endInsertRows();
 
 	// Delete oldest
-	if (commands_.size() > kMaxUndoCommands) {
+	if (commands_.size() > k_max_undo_commands) {
 		this->beginRemoveRows(QModelIndex(), 0, 0);
 		delete commands_.front().command;
 		commands_.pop_front();
 		this->endRemoveRows();
 	}
 
-	UpdateActions();
+	update_actions();
 }
 
 void UndoStack::jump(size_t index)
@@ -117,7 +117,7 @@ void UndoStack::jump(size_t index)
 
 void UndoStack::undo()
 {
-	if (CanUndo()) {
+	if (can_undo()) {
 		// Undo most recently done command
 		commands_.back().command->undo_and_set_modified();
 
@@ -128,13 +128,13 @@ void UndoStack::undo()
 		commands_.pop_back();
 
 		// Update actions
-		UpdateActions();
+		update_actions();
 	}
 }
 
 void UndoStack::redo()
 {
-	if (CanRedo()) {
+	if (can_redo()) {
 		// Redo most recently undone command
 		undone_commands_.front().command->redo_and_set_modified();
 
@@ -145,7 +145,7 @@ void UndoStack::redo()
 		undone_commands_.pop_front();
 
 		// Update actions
-		UpdateActions();
+		update_actions();
 	}
 }
 
@@ -168,25 +168,25 @@ void UndoStack::clear()
 	push(new EmptyCommand(), tr("New/Open Project"));
 }
 
-bool UndoStack::CanUndo() const
+bool UndoStack::can_undo() const
 {
 	return !commands_.empty() &&
 		   !dynamic_cast<EmptyCommand *>(commands_.back().command);
 }
 
-void UndoStack::UpdateActions()
+void UndoStack::update_actions()
 {
-	undo_action_->setEnabled(CanUndo());
-	redo_action_->setEnabled(CanRedo());
+	undo_action_->setEnabled(can_undo());
+	redo_action_->setEnabled(can_redo());
 
 	undo_action_->setText(
 		QCoreApplication::translate("UndoStack", "Undo %1")
-			.arg(CanUndo() ? commands_.back().name : QString()));
+			.arg(can_undo() ? commands_.back().name : QString()));
 	redo_action_->setText(
 		QCoreApplication::translate("UndoStack", "Redo %1")
-			.arg(CanRedo() ? undone_commands_.front().name : QString()));
+			.arg(can_redo() ? undone_commands_.front().name : QString()));
 
-	emit indexChanged(commands_.size());
+	emit index_changed(commands_.size());
 }
 
 int UndoStack::columnCount(const QModelIndex &parent) const