RFC: https://wiki.php.net/rfc/saner-numeric-strings
This removes the -1 allow_error mode from is_numeric_string functions and replaces it by
a trailing boolean out argument to preserve BC in a couple of places.
Most of the changes can be resumed to "numeric" strings which emitted a E_NOTICE now emit
a E_WARNING and "numeric" strings which emitted a E_WARNING now throw a TypeError.
This mostly affects:
- String offsets
- Arithmetic operations
- Bitwise operations
Closes GH-5762
