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/slider/base/sliderlabel.cpp

@@ -54,7 +54,7 @@ SliderLabel::SliderLabel(QWidget *parent)
 	setContextMenuPolicy(Qt::CustomContextMenu);
 }
 
-void SliderLabel::SetColor(const QColor &c)
+void SliderLabel::set_color(const QColor &c)
 {
 	// Prevent infinite loop in changeEvent when we set the stylesheet
 	override_color_enabled_ = false;
@@ -78,9 +78,9 @@ void SliderLabel::mousePressEvent(QMouseEvent *e)
 {
 	if (e->button() == Qt::LeftButton) {
 		if (e->modifiers() & Qt::AltModifier) {
-			emit RequestReset();
+			emit request_reset();
 		} else {
-			emit LabelPressed();
+			emit label_pressed();
 		}
 	}
 }
@@ -89,7 +89,7 @@ void SliderLabel::mouseReleaseEvent(QMouseEvent *e)
 {
 	if (e->button() == Qt::LeftButton) {
 		if (!(e->modifiers() & Qt::AltModifier)) {
-			emit LabelReleased();
+			emit label_released();
 		}
 	}
 }
@@ -108,7 +108,7 @@ void SliderLabel::changeEvent(QEvent *event)
 	QWidget::changeEvent(event);
 
 	if (override_color_enabled_ && event->type() == QEvent::StyleChange) {
-		SetColor(override_color_);
+		set_color(override_color_);
 	}
 }