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/render/framemanager.h

@@ -19,8 +19,8 @@
 
 ***/
 
-#ifndef FRAMEMANAGER_H
-#define FRAMEMANAGER_H
+#ifndef OAK_FRAMEMANAGER_H
+#define OAK_FRAMEMANAGER_H
 
 #include <QMutex>
 #include <QObject>
@@ -32,15 +32,15 @@ namespace olive
 class FrameManager : public QObject {
 	Q_OBJECT
 public:
-	static void CreateInstance();
+	static void create_instance();
 
-	static void DestroyInstance();
+	static void destroy_instance();
 
 	static FrameManager *instance();
 
-	static char *Allocate(int size);
+	static char *allocate(int size);
 
-	static void Deallocate(int size, char *buffer);
+	static void deallocate(int size, char *buffer);
 
 private:
 	FrameManager();
@@ -55,7 +55,7 @@ private:
    *
    * Thread-safe.
    */
-	char *AllocateFromPool(int size);
+	char *allocate_from_pool(int size);
 
 	/**
    * @brief Deallocate buffer
@@ -65,11 +65,11 @@ private:
    *
    * Thread-safe.
    */
-	void DeallocateToPool(int size, char *buffer);
+	void deallocate_to_pool(int size, char *buffer);
 
 	static FrameManager *instance_;
 
-	static const int kFrameLifetime;
+	static const int k_frame_lifetime;
 
 	struct Buffer {
 		qint64 time;
@@ -83,9 +83,9 @@ private:
 	QTimer clear_timer_;
 
 private slots:
-	void GarbageCollection();
+	void garbage_collection();
 };
 
 }
 
-#endif // FRAMEMANAGER_H
+#endif // OAK_FRAMEMANAGER_H