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/common/html.h

@@ -16,8 +16,8 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef HTML_H
-#define HTML_H
+#ifndef OAK_HTML_H
+#define OAK_HTML_H
 
 #include <QTextDocument>
 #include <QTextFragment>
@@ -45,39 +45,39 @@ namespace olive
  */
 class Html {
 public:
-	static QString DocToHtml(const QTextDocument *doc);
+	static QString doc_to_html(const QTextDocument *doc);
 
-	static void HtmlToDoc(QTextDocument *doc, const QString &html);
+	static void html_to_doc(QTextDocument *doc, const QString &html);
 
 private:
-	static void WriteBlock(QXmlStreamWriter *writer, const QTextBlock &block);
+	static void write_block(QXmlStreamWriter *writer, const QTextBlock &block);
 
-	static void WriteFragment(QXmlStreamWriter *writer,
+	static void write_fragment(QXmlStreamWriter *writer,
 							  const QTextFragment &fragment);
 
-	static void WriteCSSProperty(QString *style, const QString &key,
+	static void write_css_property(QString *style, const QString &key,
 								 const QStringList &value);
-	static void WriteCSSProperty(QString *style, const QString &key,
+	static void write_css_property(QString *style, const QString &key,
 								 const QString &value)
 	{
-		WriteCSSProperty(style, key, QStringList({ value }));
+		write_css_property(style, key, QStringList({ value }));
 	}
 
-	static void WriteCharFormat(QString *style, const QTextCharFormat &fmt);
+	static void write_char_format(QString *style, const QTextCharFormat &fmt);
 
 	static QTextCharFormat
-	ReadCharFormat(const QXmlStreamAttributes &attributes);
+	read_char_format(const QXmlStreamAttributes &attributes);
 
 	static QTextBlockFormat
-	ReadBlockFormat(const QXmlStreamAttributes &attributes);
+	read_block_format(const QXmlStreamAttributes &attributes);
 
-	static void AppendStringAutoSpace(QString *s, const QString &append);
+	static void append_string_auto_space(QString *s, const QString &append);
 
-	static QMap<QString, QStringList> GetCSSFromStyle(const QString &s);
+	static QMap<QString, QStringList> get_css_from_style(const QString &s);
 
-	static const QVector<QString> kBlockTags;
+	static const QVector<QString> k_block_tags;
 };
 
 }
 
-#endif // HTML_H
+#endif // OAK_HTML_H