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/node/gizmo/text.cpp

@@ -33,26 +33,26 @@ TextGizmo::TextGizmo(QObject *parent)
 {
 }
 
-void TextGizmo::SetRect(const QRectF &r)
+void TextGizmo::set_rect(const QRectF &r)
 {
 	rect_ = r;
-	emit RectChanged(rect_);
+	emit rect_changed(rect_);
 }
 
-void TextGizmo::UpdateInputHtml(const QString &s, const rational &time)
+void TextGizmo::update_input_html(const QString &s, const Rational &time)
 {
-	if (input_.IsValid()) {
+	if (input_.is_valid()) {
 		MultiUndoCommand *command = new MultiUndoCommand();
-		Node::SetValueAtTime(input_.input(), time, s, input_.track(), command,
+		Node::set_value_at_time(input_.input(), time, s, input_.track(), command,
 							 true);
 		Core::instance()->undo_stack()->push(command, tr("Edit Text"));
 	}
 }
 
-void TextGizmo::SetVerticalAlignment(Qt::Alignment va)
+void TextGizmo::set_vertical_alignment(Qt::Alignment va)
 {
 	valign_ = va;
-	emit VerticalAlignmentChanged(valign_);
+	emit vertical_alignment_changed(valign_);
 }
 
 }