Clean up calls to extension_loaded('json') in tests

These are no longer needed after https://wiki.php.net/rfc/always_enable_json

Closes GH-5637

Make float to string casts locale-independent

From now on, float to string casting will always behave locale-independently.
RFC: https://wiki.php.net/rfc/locale_independent_float_to_stri

Make float to string casts locale-independent

From now on, float to string casting will always behave locale-independently.
RFC: https://wiki.php.net/rfc/locale_independent_float_to_string
Closes GH-5224

Co-authored-by: George Peter Banyard <girgias@php.net>

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