Add SD theme system

Adds installable SD-card themes with manifest downloads, theme registry parsing, themed home/chrome/settings/file browser support, FreeInk layout integration, theme documentation, and layout tests.

src/ThemeInstaller.h

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <cstddef>
+
+#include "components/themes/SdCardThemeRegistry.h"
+
+class ThemeInstaller {
+ public:
+  enum class Error {
+    OK,
+    INVALID_THEME_ID,
+    INVALID_FILE,
+    SD_WRITE_ERROR,
+  };
+
+  explicit ThemeInstaller(SdCardThemeRegistry& registry);
+
+  static bool isValidThemeId(const char* id);
+  static bool isValidRelativePath(const char* path);
+  bool ensureThemeDir(const char* themeId);
+  bool ensureParentDirs(const char* fullPath);
+  bool validateThemeFile(const char* path);
+  static bool buildThemePath(const char* themeId, const char* relativePath, char* outBuf, size_t outBufSize);
+  Error deleteTheme(const char* themeId);
+  void refreshRegistry();
+  bool isThemeInstalled(const char* themeId) const;
+
+ private:
+  SdCardThemeRegistry& registry_;
+};