Feature request: use `||` to complete underfull columns

```
| I have | a table | like | this |
| and some | rows | might | be |
| | underfull
```
What I'd like is that I could just hit `||` at the end of the underfull line and it adds however many are necessary to complete the line, rather than manually having to hit however many are necessary. And for some reason, when I do just manually do it, it doesn't dot-repeat on other lines for some reason? (Maybe `tr` could do this too?)

Also to test, I visually selected the end of a couple lines, and hit `A` -- the first `|` worked on both, but the rest only on the first line.

No file or test is named. Start by reproducing the underfull-table case and the visual-selection and dot-repeat behavior described in the issue, then locate the table completion and repeat-command entry points. Done means `||` fills each underfull row to the required width and the behavior works consistently across selected lines and repeated commands.

Written by the indexing model from the issue text.