Create new sub directories for tests related to backtraces and for tests
related to `$this` being reserved in different places and not being usable or
reassignable.
Work towards GH-15631
For classes that are not declared `abstract`, produce a compiler error for any
`abstract` methods. For anonymous classes, since they cannot be made abstract,
the error message is slightly different.
Co-authored-by: Ilija Tovilo <ilija.tovilo@me.com>
Move more low-hanging fruit, creating new directories for the tests for:
* comparisons
* dynamic calls
* error messages
* `error_reporting()`
* exceptions
* `foreach()`
* garbage collection
* group `use` statements
* heredoc and nowdoc
* `goto` jumps
* late static binding
* magic methods
* namespaces
* numeric literal separators
* objects
* `settype()`
* cleaning of temporary values
* `unset()`
Additionally, move some tests into the existing subdirectory for `list()`
tests.
Drive-by fixes of some test numbers in the names of the `goto` tests.
Work towards GH-15631
