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/path/pathwidget.cpp

@@ -40,16 +40,16 @@ PathWidget::PathWidget(const QString &path, QWidget *parent)
 	path_edit_->setText(path);
 	layout->addWidget(path_edit_);
 	connect(path_edit_, &QLineEdit::textChanged, this,
-			&PathWidget::LineEditChanged);
+			&PathWidget::line_edit_changed);
 
 	browse_btn_ = new QPushButton(tr("Browse"));
 	layout->addWidget(browse_btn_);
 
 	connect(browse_btn_, &QPushButton::clicked, this,
-			&PathWidget::BrowseClicked);
+			&PathWidget::browse_clicked);
 }
 
-void PathWidget::BrowseClicked()
+void PathWidget::browse_clicked()
 {
 	QString dir = QFileDialog::getExistingDirectory(
 		static_cast<QWidget *>(parent()), tr("Browse for path"),
@@ -60,9 +60,9 @@ void PathWidget::BrowseClicked()
 	}
 }
 
-void PathWidget::LineEditChanged()
+void PathWidget::line_edit_changed()
 {
-	if (FileFunctions::DirectoryIsValid(text(), false)) {
+	if (FileFunctions::directory_is_valid(text(), false)) {
 		path_edit_->setStyleSheet(QString());
 	} else {
 		path_edit_->setStyleSheet(QStringLiteral("QLineEdit {color: red;}"));

app/widget/path/pathwidget.h

@@ -19,8 +19,8 @@
 
 ***/
 
-#ifndef PATHWIDGET_H
-#define PATHWIDGET_H
+#ifndef OAK_PATHWIDGET_H
+#define OAK_PATHWIDGET_H
 
 #include <QLineEdit>
 #include <QPushButton>
@@ -41,9 +41,9 @@ public:
 	}
 
 private slots:
-	void BrowseClicked();
+	void browse_clicked();
 
-	void LineEditChanged();
+	void line_edit_changed();
 
 private:
 	QLineEdit *path_edit_;
@@ -53,4 +53,4 @@ private:
 
 }
 
-#endif // PATHWIDGET_H
+#endif // OAK_PATHWIDGET_H