lut: pick from the global LUT library in node params; i18n; doc

- File inputs marked with the 'lut_library' property (currently the
  OCIO LUT node) now show a combo box populated from the global LUT
  library above the path field: pick a library LUT directly, or use
  'Other (Custom File)...' with the regular path field; selections go
  through the standard undoable input-change path
- Refresh zh_CN translations with lupdate and translate all strings
  introduced by the proxy dialog, LUT library, LUT picker, waveform
  sync and footage start time work
- Document the new per-footage custom <proxy> attributes and the
  'manual' source-start-time origin in the project file reference
- Add LutFileField UI tests

tests/gtest/CMakeLists.txt

@@ -46,6 +46,7 @@ add_executable(olive-gtest
   project_serializer_test.cpp
   proxy_manager_test.cpp
   proxy_dialog_test.cpp
+  lut_file_field_test.cpp
   timeline_marker_test.cpp
   undo_stack_test.cpp
   plugin_support_test.cpp

tests/gtest/lut_file_field_test.cpp

@@ -0,0 +1,107 @@
+#include <gtest/gtest.h>
+
+#include <QDir>
+#include <QFile>
+#include <QSignalSpy>
+#include <QTemporaryDir>
+
+#include "config/config.h"
+#include "render/lutlibrary.h"
+#include "widget/filefield/lutfilefield.h"
+
+namespace
+{
+
+class LutLibraryConfigGuard {
+public:
+	LutLibraryConfigGuard()
+		: previous_(olive::Config::Current()[QStringLiteral("LUTLibraryPaths")]
+						.toString())
+	{
+	}
+
+	~LutLibraryConfigGuard()
+	{
+		olive::Config::Current()[QStringLiteral("LUTLibraryPaths")] = previous_;
+	}
+
+private:
+	QString previous_;
+};
+
+QString WriteFile(const QString &path)
+{
+	QFile file(path);
+	if (!file.open(QIODevice::WriteOnly)) {
+		return QString();
+	}
+	file.close();
+	return path;
+}
+
+} // namespace
+
+TEST(LutFileField, PopulatesComboFromLibrary)
+{
+	LutLibraryConfigGuard guard;
+
+	QTemporaryDir dir;
+	ASSERT_TRUE(dir.isValid());
+
+	const QString cube =
+		WriteFile(QDir(dir.path()).filePath(QStringLiteral("a.cube")));
+	const QString three_dl =
+		WriteFile(QDir(dir.path()).filePath(QStringLiteral("b.3dl")));
+	const QString other =
+		WriteFile(QDir(dir.path()).filePath(QStringLiteral("c.txt")));
+	ASSERT_FALSE(cube.isEmpty());
+	ASSERT_FALSE(three_dl.isEmpty());
+	ASSERT_FALSE(other.isEmpty());
+
+	olive::LUTLibrary::SetDirectories({ dir.path() });
+
+	olive::LutFileField field;
+
+	// One "Other" entry plus one entry per supported LUT
+	ASSERT_EQ(field.library_combo()->count(), 3);
+	EXPECT_TRUE(field.library_combo()->itemData(0).toString().isEmpty());
+	EXPECT_GE(field.library_combo()->findData(cube), 1);
+	EXPECT_GE(field.library_combo()->findData(three_dl), 1);
+	EXPECT_EQ(field.library_combo()->findData(other), -1);
+}
+
+TEST(LutFileField, SelectionFollowsFilenameAndEmitsOnPick)
+{
+	LutLibraryConfigGuard guard;
+
+	QTemporaryDir dir;
+	ASSERT_TRUE(dir.isValid());
+
+	const QString cube =
+		WriteFile(QDir(dir.path()).filePath(QStringLiteral("a.cube")));
+	ASSERT_FALSE(cube.isEmpty());
+
+	olive::LUTLibrary::SetDirectories({ dir.path() });
+
+	olive::LutFileField field;
+
+	// A path that is not in the library shows the "Other" entry
+	field.SetFilename(QStringLiteral("/custom/elsewhere.cube"));
+	EXPECT_EQ(field.library_combo()->currentIndex(), 0);
+
+	// A library path selects its entry
+	field.SetFilename(cube);
+	EXPECT_GT(field.library_combo()->currentIndex(), 0);
+
+	// Picking a library entry updates the filename and emits the change
+	// signal so the parameter bridge applies it like any other edit
+	field.SetFilename(QString());
+	QSignalSpy spy(&field, &olive::FileField::FilenameChanged);
+	const int index = field.library_combo()->findData(cube);
+	ASSERT_GE(index, 1);
+	emit field.library_combo()->activated(index);
+
+	EXPECT_EQ(field.GetFilename(), cube);
+	ASSERT_EQ(spy.count(), 1);
+	EXPECT_EQ(spy.first().first().toString(), cube);
+}