function getLeftDeleteOffset(offset, str) {
    if (offset === 0) {
        return 0;
    }
    // Try to delete emoji part.
    const emojiOffset = getOffsetBeforeLastEmojiComponent(offset, str);
    if (emojiOffset !== undefined) {
        return emojiOffset;
    }
    // Otherwise, just skip a single code point.
    const iterator = new CodePointIterator(str, offset);
    iterator.prevCodePoint();
    return iterator.offset;
}
Computes the offset after performing a left delete on the given string,
while considering unicode grapheme/emoji rules.