Constrain number parameter of numfmt_format to int|float

Constrain number parameter of numfmt_format to int|float

This is inline with similar changes to the math functions.  Especially,
array to number conversion makes no sense here, and is likely to hide
a programming error.

To make that feasible, we introduce the `n` specifier for classic ZPP
so we can stick with `zend_parse_method_parameters()`.

We also remove a test case, which has been degenerated to a ZPP test.