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

Closes GH-5590

Closes GH-5221

Remove duplicate test (iterator_018.phpt)

This is exactly the same as iterator_011.phpt.

Remove duplicate test (offsets_chaining_2.phpt)

This is exactly the same as offsets_chaining_1.phpt.

Remove duplicate test (offsets_chaining_4.phpt)

This is exactly the same as offsets_chaining_3.phpt.

Remove duplicate test (ReflectionObject_export_basic1.phpt)

This is exactly the same as ReflectionObject___toString_basic1.phpt.

Remove duplicate test (ReflectionObject_export_basic2.phpt)

This is exactly the same as ReflectionObject___toString_basic2.phpt.

Closes GH-5467.

Closes GH-4837.

RFC: https://wiki.php.net/rfc/deprecate_curly_braces_array_access

This is part of https://wiki.php.net/rfc/deprecations_php_7_3.