fix(style): for imgsrc type

[cnjhb]

lvgl does not preserve the passed string. Therefore, it needs to be saved on the Lua side.

[XuNeo]

LVGL will save the pointer in struct lv_image_t directly, thus it's useable when obj is alive.
Have you met some issues with it?

[cnjhb]

LVGL will save the pointer in struct lv_image_t directly, thus it's useable when obj is alive. Have you met some issues with it?

lv_image will store the entire string. But style will only store pointers. Probably because of lua's memory defragmentation, the stored pointers become invalid after a while.