Migrate skip checks to --EXTENSIONS--, p3

For rationale, see #6787

Extensions migrated in part 3:
* ftp
* gmp
* iconv
* opcache
* shmop

Backport preloading trait fixup fixes

This cherry-picks 33969c2252b2c33a72c9039072af8862fd347a5f and
2effbfd8713936742ef46e6e85ce193b320ac005 from PHP-8.0.

The issues these comm

Backport preloading trait fixup fixes

This cherry-picks 33969c2252b2c33a72c9039072af8862fd347a5f and
2effbfd8713936742ef46e6e85ce193b320ac005 from PHP-8.0.

The issues these commits fix could also manifest in PHP 7.4, and
a commenter on bug #80307 reports this this might indeed be
happening.

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Fixup trait methods even if no traits are used

Trait methods might be non-trivially inherited, in which case we
may have to perform fixup in classes that do not directly use any
trai

Fixup trait methods even if no traits are used

Trait methods might be non-trivially inherited, in which case we
may have to perform fixup in classes that do not directly use any
traits.

show more ...

Fix multiple trait fixup

If a trait method is inherited, preloading trait fixup might be
performed on it multiple times. Usually this is fine, because
the opcodes pointer will have a

Fix multiple trait fixup

If a trait method is inherited, preloading trait fixup might be
performed on it multiple times. Usually this is fine, because
the opcodes pointer will have already been updated, and will thus
not be found in the xlat table.

However, it can happen that the new opcodes pointer is the same
as one of the old opcodes pointers, if the pointer has been reused
by the allocator. In this case we will look up the wrong op array
and overwrite the trait method with an unrelated trait method.

We fix this by indexing the xlat table not by the opcodes pointer,
but by the refcount pointer. The refcount pointer is not changed
during optimization, and accurately represents which op arrays
should use the same opcodes.

Fixes bug #80307. The test case does not reproduce the bug, because
this depends on a lot of "luck" with the allocator. The test case
merely illustrates a case where orig_op_array would have been NULL
in the original code.

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