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/widget/menu/menu.cpp

@@ -30,29 +30,29 @@ Menu::Menu(QMenuBar *bar)
 {
 	bar->addMenu(this);
 
-	Init();
+	init();
 }
 
 Menu::Menu(Menu *menu)
 {
 	menu->addMenu(this);
 
-	Init();
+	init();
 }
 
 Menu::Menu(QWidget *parent)
 	: QMenu(parent)
 {
-	Init();
+	init();
 }
 
 Menu::Menu(const QString &s, QWidget *parent)
 	: QMenu(s, parent)
 {
-	Init();
+	init();
 }
 
-QAction *Menu::AddActionWithData(const QString &text, const QVariant &d,
+QAction *Menu::add_action_with_data(const QString &text, const QVariant &d,
 								 const QVariant &compare)
 {
 	QAction *a = addAction(text);
@@ -64,14 +64,14 @@ QAction *Menu::AddActionWithData(const QString &text, const QVariant &d,
 	return a;
 }
 
-QAction *Menu::InsertAlphabetically(const QString &s)
+QAction *Menu::insert_alphabetically(const QString &s)
 {
 	QAction *action = new QAction(s, this);
-	InsertAlphabetically(action);
+	insert_alphabetically(action);
 	return action;
 }
 
-void Menu::InsertAlphabetically(QAction *entry)
+void Menu::insert_alphabetically(QAction *entry)
 {
 	QList<QAction *> actions = this->actions();
 
@@ -85,12 +85,12 @@ void Menu::InsertAlphabetically(QAction *entry)
 	addAction(entry);
 }
 
-void Menu::InsertAlphabetically(Menu *menu)
+void Menu::insert_alphabetically(Menu *menu)
 {
-	InsertAlphabetically(menu->menuAction());
+	insert_alphabetically(menu->menuAction());
 }
 
-void Menu::ConformItem(QAction *a, const QString &id, const QKeySequence &key)
+void Menu::conform_item(QAction *a, const QString &id, const QKeySequence &key)
 {
 	a->setProperty("id", id);
 
@@ -103,7 +103,7 @@ void Menu::ConformItem(QAction *a, const QString &id, const QKeySequence &key)
 	}
 }
 
-void Menu::Init()
+void Menu::init()
 {
 	// HACK: Disables embossing on disabled text for a slightly nicer UI
 	QPalette p = palette();