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/decibel.h

@@ -19,8 +19,8 @@
 
 ***/
 
-#ifndef DECIBEL_H
-#define DECIBEL_H
+#ifndef OAK_DECIBEL_H
+#define OAK_DECIBEL_H
 
 #include <QtGlobal>
 #include <cmath>
@@ -33,20 +33,20 @@ namespace olive
 class Decibel {
 public:
 	// In basically all circumstances, this should calculate to 0.0 linear
-	static constexpr double MINIMUM = -200.0;
+	static constexpr double minimum = -200.0;
 
-	static double fromLinear(double linear)
+	static double from_linear(double linear)
 	{
 		double v = double(20.0) * std::log10(linear);
 #ifndef ALLOW_RETURNING_INFINITY
 		if (std::isinf(v)) {
-			return MINIMUM;
+			return minimum;
 		}
 #endif
 		return v;
 	}
 
-	static double toLinear(double decibel)
+	static double to_linear(double decibel)
 	{
 		double to_linear = std::pow(double(10.0), decibel / double(20.0));
 
@@ -58,47 +58,47 @@ public:
 		}
 	}
 
-	static double fromLogarithmic(double logarithmic)
+	static double from_logarithmic(double logarithmic)
 	{
 		if (logarithmic < 0.001)
 #ifdef ALLOW_RETURNING_INFINITY
 			return std::numeric_limits<double>::infinity();
 #else
-			return MINIMUM;
+			return minimum;
 #endif
 		else if (logarithmic > 0.99)
 			return 0;
 		else
-			return 20.0 * std::log10(-std::log(1 - logarithmic) / LOG100);
+			return 20.0 * std::log10(-std::log(1 - logarithmic) / lo_g100);
 	}
 
-	static double toLogarithmic(double decibel)
+	static double to_logarithmic(double decibel)
 	{
 		if (qFuzzyIsNull(decibel)) {
 			return 1;
 		} else {
-			return 1 - std::exp(-std::pow(10.0, decibel / 20.0) * LOG100);
+			return 1 - std::exp(-std::pow(10.0, decibel / 20.0) * lo_g100);
 		}
 	}
 
-	static double LinearToLogarithmic(double linear)
+	static double linear_to_logarithmic(double linear)
 	{
-		return 1 - std::exp(-linear * LOG100);
+		return 1 - std::exp(-linear * lo_g100);
 	}
 
-	static double LogarithmicToLinear(double logarithmic)
+	static double logarithmic_to_linear(double logarithmic)
 	{
 		if (logarithmic > 0.99) {
 			return 1;
 		} else {
-			return -std::log(1 - logarithmic) / LOG100;
+			return -std::log(1 - logarithmic) / lo_g100;
 		}
 	}
 
 private:
-	static constexpr double LOG100 = 4.60517018599;
+	static constexpr double lo_g100 = 4.60517018599;
 };
 
 }
 
-#endif // DECIBEL_H
+#endif // OAK_DECIBEL_H