Draft: Initial merged cells support in `get_cells()`

[tzakharko]

Initial implementation for #289

This adds new columns n_rows and n_cols to the result of get_cells()/range_read_cells(). API response with the merged cell ranges is parsed in get_merged_ranges() and then left-joined by starting location into the cell table.

No updates to documentation, tests, or range formatting yet. Could also use error handling when implementing the join.

[jennybc]

I assume you've got a test sheet or two lying around with some merged cells that you are developing against.... can you share with "anyone with a link"? And share the ID here? Then I could experience this for myself. I can't really work on this feature right now, so to advance things, I have to be able to make intelligent comments with a modest amount of time/psychic energy.

[tzakharko]

Absolutely! Here a simple example sheet

devtools::load_all()

range_read_cells(
  "https://docs.google.com/spreadsheets/d/1wDJKdfSyvi2CCr-ZBzWslo4HQLsGAaMwpalAiq6KHws",
  discard_empty = TRUE
) %>%
dplyr::mutate(cell = purrr::map_chr(cell, "formattedValue"))

And the output

row	col	n_rows	n_cols	loc	cell
1	1	1	1	A1	A1
2	2	1	1	B2	B2
3	1	1	1	A3	B3
4	2	2	2	B4	merged B4:C5
6	3	1	1	C6	C6
7	1	1	3	A7	merged A7:C7
8	1	1	1	A8	A8
9	1	3	1	A9	merged A9:A11
9	2	1	1	B9	B9
11	2	1	1	B11	B11

If you can just have a quick look and tell me whether you are ok with the general direction, I'd be happy to also add tests, documentation, missing checks etc. I kept it minimal on purpose for now. Thanks for your time!