eclass: php-ext-sources-r3 - Apply user patches to all targets

eclass: php-ext-sources-r3 - Apply user patches to all targets

The original eclass copied sources as part of the exported src_unpack
and then attempted to apply default_src_prepare to every PHP_TARGET.

As the bug shows, this fails on eapply_user because that function will
only ever apply once.

Instead, eliminate the php-ext-sources-r3_src_unpack. Move the copy
function to src_prepare phase after patches were applied,
optionally disabled by PHP_EXT_SKIP_PATCHES=yes.

This eclass will only apply patches to PHP_EXT_S.

Fixes: https://bugs.gentoo.org/650324