Improve modelling of `AsyncResumedDef` store in value numbering

[jakobbotsch]

In VN we set the value of all call defs to unknown here:

runtime/src/coreclr/jit/valuenum.cpp

Lines 14952 to 14962 in 72dac24

	// If the call generates any definitions, for example because it uses "return buffer", then VN the local
	// as well.
	auto visitDef = [=](const LocalDef& def) {
	ValueNumPair storeValue;
	storeValue.SetBoth(vnStore->VNForExpr(compCurBB, lvaGetDesc(def.Def->AsLclVarCommon())->TypeGet()));
	fgValueNumberLocalStore(call, def.Def, def.Offset, def.Size, storeValue);
	return GenTree::VisitResult::Continue;
	};
	call->VisitLocalDefs(this, visitDef);

However, in two scenarios we do know the value of AsyncResumedDef:

1. If this is an always-suspending call, then the value will be 1 after
2. If this is dominated by an always-suspending call (i.e. resumed is already known to be constant 1) then the value will also be 1 after

We should be able to model this.

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