alias tile_background -> grid_background

BUR #22795 has been approved by @nonamethanks.

create alias tile_background -> grid_background

Tile background's wiki was deleted four years ago but nothing was ever done with it, and people currently use it in lieu of grid background, checkered background, and even argyle background. The BUR is to grid background because that's the most frequent case, but a deprecation is also a good idea.

On the topic of grid background, how valid of an idea is multicolored_grid_background? The vast majority of the former are a single color unlike post #4008891, so it seems valuable to make a spinoff tag.

The bulk update request #22795 (forum #266762) has been approved by @nonamethanks.