devtools

b083abb4 - Add button for toggling background colour during raster preview (#6827)

Add button for toggling background colour during raster preview (#6827)  This PR adds a toggle button to the layer view widget. The toggle button cycles the background of the preview through grey, black, and white backgrounds. This can be helpful if it is difficult to make out the layer if the background doesn't provide enough contrast Fixes https://github.com/flutter/devtools/issues/5660 <img width="941" alt="Screenshot 2023-11-28 at 3 11 16 PM" src="https://github.com/flutter/devtools/assets/1386322/c0476a3e-1803-4d2a-8b78-43c43d6e582a"> <img width="942" alt="Screenshot 2023-11-28 at 3 11 09 PM" src="https://github.com/flutter/devtools/assets/1386322/66f752cd-c011-4fb0-bfc1-7975f0ba1f8b"> <img width="1163" alt="Screenshot 2023-11-28 at 3 11 04 PM" src="https://github.com/flutter/devtools/assets/1386322/3a62eeab-5f06-4c99-9926-22111192efe5"> <img width="1167" alt="Screenshot 2023-11-28 at 3 10 58 PM" src="https://github.com/flutter/devtools/assets/1386322/2169c2ac-7264-4e41-9724-fe6b0b204df7">