I would think twice about continuing much past the edge of the tub flood rim and wile there may not be specific trim, there are any number of decorative molding as well as decorative features to break the monotony of the field.

What does the other end of the tub look like? I would want to maintain some sort of symmetry.

I suggest extending it outside the tub a couple inches at least (and down to the baseboard). If it's real stone, you could look into having the edges ground or polished for the number of pieces you need. (done ahead of time). Or you could use schluter rondec or similar.

Ideally, I would take it to the edge of the corner with some trim or, as homebound said, if it's real stone find someone to grind the edges so that you have a bullnose. If you choose not to go to the edge, I would come out several inches past the edge of the tub, especially if you intend to install a shower door or curtain.
Here's a pic of how the builder finished my guest bathroom. Gives you a visual of 'not going to the edge'.

Some pics on how we did it. In the first photo, the tile does not wrap around to the toilet side. It is painted on that side.

In this photo the tile connects to the tile in the shower.

Thank you so much. You guys are great. I guess that's a good use for the Schluter edge trim? I'll find a sample of it.