Send :fiber_switch event for almost every fiber_switch (#4207)

With this patch, TracePoint receives a `:fiber_switch` event for
_almost_ every fiber switch.  Previously, it would not be sent when an
exception was going to be raised. Now the event should only be blockable
by an interrupt (including `Thread#raise`) or a fatal error.

Additionally, interrupts will now be checked on the return fiber
_before_ re-raising the terminating unhandled exception.  And a fiber
that terminates with an unhandled exception no longer creates a pending
interrupt on its thread.  The exception will be raised in the return
fiber the same way as `Fiber#raise`: using `cont.value` with `cont.argc
== -1`

I moved `rb_exc_raise` from `fiber_store` to the end of `fiber_switch`
after _all_ of the other cleanup code: `fiber_stack_release`,
`th->blocking` increment, `RUBY_VM_CHECK_INTS`, and `EXEC_EVENT_HOOK`.
It seems to me that skipping those other cleanup steps may have also
resulted in other bugs.

0 files changed, 0 insertions, 0 deletions