Refactor Tile16Editor drawing logic and enhance tile handling

- Updated the DrawToCurrentTile16 method to accept an optional source tile parameter, improving flexibility in tile rendering.
- Refined the logic for regenerating tile16 bitmaps from ROM data, ensuring accurate updates and palette management.
- Enhanced the UI layout for the Tile16 editor, optimizing the interaction of tile8 and tile16 controls.
- Improved code readability by standardizing formatting and reducing unnecessary whitespace.

src/app/editor/overworld/tile16_editor.h

@@ -54,7 +54,7 @@ class Tile16Editor : public gfx::GfxContext {
   absl::Status SaveLayoutToScratch(int slot);
   absl::Status LoadLayoutFromScratch(int slot);
 
-  absl::Status DrawToCurrentTile16(ImVec2 pos);
+  absl::Status DrawToCurrentTile16(ImVec2 pos, const gfx::Bitmap* source_tile = nullptr);
 
   absl::Status UpdateTile16Edit();