This function has two signatures:
Returns the index within text string of the rightmost occurrence of the toFind substring.
The search starts from fromOffset index. Returns the index within text string of the last occurrence of the toFind substring, searching backwards starting from the fromOffset index.
oxy_lastindexof('abcdbc', 'bc') returns 4.
oxy_lastindexof('abcdbccdbc', 'bc', 2) returns 1.