bisect--helper: `bisect_next_check` shell function in C

bisect--helper: `bisect_next_check` shell function in C

Reimplement `bisect_next_check` shell function in C and add
`bisect-next-check` subcommand to `git bisect--helper` to call it from
git-bisect.sh .

`bisect_voc` shell function is no longer useful now and is replaced by
using a char *[] of "new|bad" and "good|old" values.

Using `--bisect-next-check` is a temporary measure to port shell
function to C so as to use the existing test suite. As more functions
are ported, this subcommand will be retired but its implementation will
be called by some other methods.

Helped-by: Stephan Beyer <redacted>
Mentored-by: Lars Schneider <redacted>
Mentored-by: Christian Couder <redacted>
Mentored-by: Johannes Schindelin <redacted>
Signed-off-by: Pranit Bauva <redacted>
Signed-off-by: Tanushree Tumane <redacted>
Signed-off-by: Junio C Hamano <redacted>