The Windows VEH is a process-wide first-chance handler and #355 used it as
a catch-all for every access violation on a parallel worker. Narrowing it
unmasked a latent shutdown access violation in functional/007 (bootstrap
set inside a task) that crashes the process. That is a separate, Windows-only
issue that needs a Windows repro to fix properly, so restore the VEH to its
original catch-all behavior.

The undefined-function narrowing (and the debugging benefit of not masking
real crashes under sanitizers/gdb/core dumps) remains on the POSIX SIGSEGV
handler, which is where it matters.

The SIGSEGV/VEH handler added in #355 caught *every* fault on a parallel
worker thread and converted it into a catchable IllegalInstruction error
via zend_bailout(). This masked genuine bugs (no backtrace, no core dump)
and longjmp-ing out of a signal handler is not async-signal-safe.

Restrict the conversion to the single case it was built for: a worker
faulting on a ZEND_INIT_FCALL to a function that is not in the worker's
function table (i.e. not provided via a bootstrap file). Any other fault
now falls through to the previous handler so it crashes properly with a
backtrace / core dump.

Detection is factored into php_parallel_scheduler_recover_missing_function()
shared by both the POSIX and Windows handlers.

The SIGSEGV/VEH handler added in #355 caught *every* fault on a parallel
worker thread and converted it into a catchable IllegalInstruction error
via zend_bailout(). This masked genuine bugs (no backtrace, no core dump)
and longjmp-ing out of a signal handler is not async-signal-safe.

Restrict the conversion to the single case it was built for: a worker
faulting on a ZEND_INIT_FCALL to a function that is not in the worker's
function table (i.e. not provided via a bootstrap file). Any other fault
now falls through to the previous handler so it crashes properly with a
backtrace / core dump.