Second pass through `Zend/tests/bug*` to organize the tests.
Move tests to existing sub directories, and create some new sub directories:
* `ArrayAccess`
* `autoload`
* `clone`
* `serialize` (also covers `unserialize()`)
* `switch`
Work towards GH-15631
Unlike the `userland_declaration_error_const.phpt` test, the point of this test
is to demonstrate using a class constant as the default parameter. See also the
corresponding internal_declaration_* tests.
[skip ci]
Closes GH-5353. From now on, PHP will have reflection information
about default values of parameters of internal functions.
Co-authored-by: Nikita Popov <nikita.ppv@gmail.com>