Move trap handler initialization to per-Store (#1644)

Previously we initialized trap handling (signals/etc) once-per-instance
but that's a bit too granular since we only need to do this as
one-time per-program initialization. This moves the initialization to
`Store` instead which means that we'll call this at least once per
thread, which some platforms may need (none currently do, they all only
need per-program initialization, but Fuchsia will need per-thread
initialization).

crates/runtime/src/instance.rs

@@ -7,7 +7,6 @@ use crate::imports::Imports;
 use crate::jit_int::GdbJitImageRegistration;
 use crate::memory::{DefaultMemoryCreator, RuntimeLinearMemory, RuntimeMemoryCreator};
 use crate::table::Table;
-use crate::traphandlers;
 use crate::traphandlers::Trap;
 use crate::vmcontext::{
     VMBuiltinFunctionsArray, VMCallerCheckedAnyfunc, VMContext, VMFunctionBody, VMFunctionImport,
@@ -886,10 +885,6 @@ impl InstanceHandle {
         );
         *instance.interrupts() = &*instance.interrupts;
 
-        // Ensure that our signal handlers are ready for action.
-        // TODO: Move these calls out of `InstanceHandle`.
-        traphandlers::init();
-
         // Perform infallible initialization in this constructor, while fallible
         // initialization is deferred to the `initialize` method.
         initialize_passive_elements(instance);