The variable size of zend_fiber_stack results in the offset of other fields to be variable, which causes compatiblity issues with extensions when php-src is compiled with ASan enabled. This solution was prefered over moving the stack field to be the last member, as inclusion of ZEND_FIBER_CONTEXT_FIELDS into other structs may still result in field offset errors.
The definition of zend_fiber_stack was removed from the header to hide it from the ABI.
Renamed prior_pointer and prior_size to asan_pointer and asan_size to reflect their current use.
Changed context flags type to uint8_t.
Renamed valgrind stack id field to valgrind_stack_id and fixed the type to unsigned int.
This additional internal fiber API creates and manipulates a Fiber object, allowing any internal function to start, resume, or suspend a fiber. The existing zend_fiber_context API allows custom C-based fiber creation using the bundled switching context, but does not interact with the PHP VM. This API behaves the same as calling Fiber object methods from user code, switching EGs, and triggering the fiber switch observer. In general, the Fiber object methods call these new API methods.
This removes switching to main for fatal errors in fibers in favor of catching any zend_bailout in a fiber and calling zend_bailout again after switching to the previous fiber or {main}.
This is needed by both fibers and opcache (and GH-6903 also uses it),
so make it a common structure that can be used by any functionality
storing warnings/errors.
