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.

tests/gtest/common_current_test.cpp

@@ -1,6 +1,6 @@
 #include <gtest/gtest.h>
 
-#include "common/Current.h"
+#include "common/current.h"
 #include "render/videoparams.h"
 #include "olive/core/render/audioparams.h"
 
@@ -12,7 +12,7 @@ TEST(CommonCurrent, SetAndGetVideoParams)
 	Current::getInstance().setCurrentVideoParams(params);
 
 	const olive::VideoParams &stored =
-		Current::getInstance().currentVideoParams();
+		Current::getInstance().current_video_params();
 	EXPECT_EQ(stored.width(), 1920);
 	EXPECT_EQ(stored.height(), 1080);
 }
@@ -24,6 +24,6 @@ TEST(CommonCurrent, SetAndGetAudioParams)
 	Current::getInstance().setCurrentAudioParams(params);
 
 	const olive::AudioParams &stored =
-		Current::getInstance().currentAudioParams();
+		Current::getInstance().current_audio_params();
 	EXPECT_EQ(stored.sample_rate(), 48000);
 }