New game: normal/unboxed sudoku i.e. without sub-blocks?

[goyalyashpal]

Is your feature request related to a problem? To play the game of sudoku but without the constraint of sub-blocks (those 3x3 boxes in the 9x9 main grid)

Describe the solution you'd like Add a new game

Describe alternatives you've considered

• (i considered) Adding this capability in the existing game of solo,
• but seeing the "custom game generation/configuration" panel for solo, it seems to me that the current implementation of solo is centered around the sub-blocks
• or maybe it's just that custom config panel, i don't know

https://www.chiark.greenend.org.uk/~sgtatham/puzzles/js/solo

Additional context #564 will become super easy after this