Support clearing existing text

support/include/FontWriter/font_writer.hpp

@@ -34,6 +34,8 @@ namespace JabyEngine {
             FontWriter::setup(vram_dst, Make::SizeI16(font_info.font_size.width, font_info.font_size.height));
         }
 
+        void clear();
+
         void write(State& state, const char* str, ...) {
             __write_impl(str, GPU::Color24::Grey(), nullptr);
         }