Repeat questions don't show up in the data table

[raphmim]

This makes it impossible to filter/search based on the answers to the repeat questions

[raphmim]

@jnm @magicznyleszek thanks for working on this issue! Can I help with testing or designing?

[duvld]

From my discussion with @magicznyleszek, PR #2650 (merged now) covers the following:

• repeat groups in table: show up as text list
• repeat groups in submission modal: works
• repeat groups matrix in submission modal: works

It does not cover:

• repeat groups matrix in table: doesn't work
  Blocked by a design/display issue -- we don't know the best way to display repeated matrix questions

[jnm]

We need to figure out why matrices aren't working, as they're not different from other repeating groups (except that they're handled specially in the form builder).