split: with --line-bytes only allocate memory as needed

split: with --line-bytes only allocate memory as needed

* src/split.c (line_bytes_split): Rewrite to only buffer
when necessary.  I.E. only increase the buffer when we've
already lines output in a split and we encounter a line
larger than the input buffer size, in which case a hold
buffer will be increased in increments of the input buffer size.
(lines_rr): Use the more abstract xalloc_die() just like
we did in line_bytes_split(), rather than explicitly
printing the "memory exhausted" message and exiting.
* tests/split/line-bytes.sh: Add a new test for this
function which previously had no test coverage.
* tests/local.mk: Reference the new test.
* NEWS: Mention the improvement.
Fixes http://bugs.gnu.org/13537