Add new system functions to row-wise and column-wise tables

[pmikkelsen]

The new ⎕SHELL, ⎕VGET and ⎕VSET system functions need to be added to the tables at https://dyalog.github.io/documentation/20.0/language-reference-guide/system-functions/system-functions-and-variables-rowwise/ and https://dyalog.github.io/documentation/20.0/language-reference-guide/system-functions/system-functions-and-variables-colwise/

As the tables are currently full, they need to grow in some direction. I don't know which direction looks best.

[xpqz]

We cope with vertical growth much better than horizontal, but the presentation is sub-optimal either way.