function find_unescaped_char(string, search_start_index, char) {
	let i = search_start_index;
	while (true) {
		const found_index = string.indexOf(char, i);
		if (found_index === -1) {
			return Infinity;
		}
		if (count_leading_backslashes(string, found_index - 1) % 2 === 0) {
			return found_index;
		}
		i = found_index + 1;
	}
}
@param {string} string The string to search.
@param {number} search_start_index The index to begin the search at.
@param {string} char The character to search for.
@returns {number} The index of the first unescaped instance of {@link char}, or `Infinity` if not found.