splitOnLastStarter

splitOnLastStarter($normalized): two strings, the part before the last starter (a character of combining class 0) and the rest. The rest may still change when more text follows, so text normalized in pieces is put together as:

my ($done, $pending) = splitOnLastStarter($normalized);
my $all = $done . NFC($pending . $more);

$normalized must already be in the form being built. normalize_partial wraps this.