Support range for large @-mention files

[abeatrix]

Large files are disabled in @-mentions but that also removes the ability to choose range for the large files.

We should update to support that.

Also noticed a regression (compared to the old @-mention) where the range doesn't show up until you have completed typing:

[PriNova]

Thanks @abeatrix for raising this issue here. This is the best place for tracking it. My bad to append it on a closed PR.

[abeatrix]

@PriNova no problem at all! Thanks for flagging the issue!