Fix the bug in php c extension that setting one field can change another field's value. (#3455)

* Fix the bug in php c extension that setting one field can change another
field's value.

The reason is that previously, in c extension, it was assumed that the
order that fields were declared in php is the same as the order of
fields in upb. This is not true. Now, for every field in upb, we will
look up the actual property that is corresponding to the upb field.

* Cleanup pull request

* Fix indentation

* Port to php5

* Port with php7.1

* Port to zts