Re: [PATCH v3 5/6] t/helper/test-json-writer.c: avoid using `strtok()`

> Apply similar treatment as in the previous commit to remove usage of
> `strtok()` from the "oidmap" test helper.
> 
> Each of the different commands that the "json-writer" helper accepts
> pops the next space-delimited token from the current line and interprets
> it as a string, integer, or double (with the exception of the very first
> token, which is the command itself).
> 
> To accommodate this, split the line in place by the space character, and
> pass the corresponding string_list to each of the specialized `get_s()`,
> `get_i()`, and `get_d()` functions.
> 
> `get_i()` and `get_d()` are thin wrappers around `get_s()` that convert
> their result into the appropriate type by either calling `strtol()` or
> `strtod()`, respectively. In `get_s()`, we mark the token as "consumed"
> by incrementing the `consumed_nr` counter, indicating how many tokens we
> have read up to that point.
> 
> Because each of these functions needs the string-list parts, the number
> of tokens consumed, and the line number, these three are wrapped up in
> to a struct representing the line state.
> 
> Signed-off-by: Taylor Blau <me@ttaylorr.com>