Changeset 49193

Coding Standards: Replace alias PHP functions with the canonical names.

Using the canonical function name for PHP functions is strongly recommended, as aliases may be deprecated or removed without (much) warning.

This replaces all uses of the following:

• join() with implode()
• sizeof() with count()
• is_writeable() with is_writable()
• doubleval() with a (float) cast

In part, this is a follow-up to #47746.

Props jrf.
See #50767.