Don't store Arc<VMInterrupts> in instances

Similar to other data structures owned by the `Store` there's no need
for `Instance` to have a strong `Arc` reference, instead it's sufficient
for `Store` to have the owning reference.

crates/runtime/src/traphandlers.rs

@@ -453,8 +453,8 @@ impl<'a> CallThreadState<'a> {
             UnwindReason::JitTrap { backtrace, pc } => {
                 debug_assert_eq!(ret, 0);
                 let maybe_interrupted = unsafe {
-                    (*self.vmctx).instance().interrupts.stack_limit.load(SeqCst)
-                        == wasmtime_environ::INTERRUPTED
+                    let interrupts = (*self.vmctx).instance().interrupts();
+                    (**interrupts).stack_limit.load(SeqCst) == wasmtime_environ::INTERRUPTED
                 };
                 Err(Trap::Jit {
                     pc,