Return `TableOutput` struct from `TableBuilder::body()`

[KYovchevski]

Currently it appears to be impossible, or very difficult, to receive information about the table that will be drawn to the window. This PR adds a barebones solution to this by returning a TableOutput struct from fn body() which describes the basic details about the header and the content body of the table.

I'm ok with spending the extra time to expand this further to cover more of the data about the table, such as being able to return values from the header and body functions, or being able to specify the sense on them. However, I want to verify this is the preferred way of doing this beforehand.

[emilk]

I'm not sure why the CI isn't kicking in. Perhaps try merging in latest master and see if it helps?

[KYovchevski]

I'm not sure why the CI isn't kicking in. Perhaps try merging in latest master and see if it helps?

I just finished a rebase on top of master, and it seems to require approval from a maintainer to run the CI.

[emilk]

Looks good, except for the missing newline

[emilk]

bump! I cannot commit my suggested change

[emilk]

also needs merge of master