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/ffmpegutils.h

@@ -19,8 +19,8 @@
 
 ***/
 
-#ifndef FFMPEGABSTRACTION_H
-#define FFMPEGABSTRACTION_H
+#ifndef OAK_FFMPEGABSTRACTION_H
+#define OAK_FFMPEGABSTRACTION_H
 
 #include <ffmpeg_bridge/ffmpeg_bridge.h>
 
@@ -50,29 +50,29 @@ public:
    * taking a single argument, an unscoped enum argument would silently
    * prefer an int overload over the PixelFormat one.
    */
-	static int GetCompatibleBridgePixelFormat(
-		int pix_fmt, PixelFormat maximum = PixelFormat::INVALID);
+	static int get_compatible_bridge_pixel_format(
+		int pix_fmt, PixelFormat maximum = PixelFormat::invalid);
 
 	/**
    * @brief Returns a native pixel format that can be used to convert from a native frame to a bridge frame with minimal data loss
    */
-	static PixelFormat GetCompatiblePixelFormat(const PixelFormat &pix_fmt);
+	static PixelFormat get_compatible_pixel_format(const PixelFormat &pix_fmt);
 
 	/**
    * @brief Returns a bridge pixel format for a given native pixel format
    */
-	static int GetFFmpegPixelFormat(const PixelFormat &pix_fmt,
+	static int get_f_fmpeg_pixel_format(const PixelFormat &pix_fmt,
 									int channel_layout);
 
 	/**
    * @brief Returns a native sample format type for a given bridge sample format
    */
-	static SampleFormat GetNativeSampleFormat(int smp_fmt);
+	static SampleFormat get_native_sample_format(int smp_fmt);
 
 	/**
    * @brief Returns a bridge sample format type for a given native type
    */
-	static int GetFFmpegSampleFormat(const SampleFormat &smp_fmt);
+	static int get_f_fmpeg_sample_format(const SampleFormat &smp_fmt);
 
 	/**
    * @brief Convert "JPEG"/full-range colorspace to its regular counterpart
@@ -81,9 +81,9 @@ public:
    * time being, FFmpeg still uses these JPEG spaces, so for simplicity (since we *are* color_range
    * aware), we use this function.
    */
-	static int ConvertJPEGSpaceToRegularSpace(int f);
+	static int convert_jpeg_space_to_regular_space(int f);
 };
 
 }
 
-#endif // FFMPEGABSTRACTION_H
+#endif // OAK_FFMPEGABSTRACTION_H