[Stack Switching] Support cross-module coroutine calls in the interpreter (#7797)

Key changes:

* In ContData, store a function Literal, not a name. The literal, same as used
  for function references since #7787, contains logic for cross-module calls.
* Store continuation state in a shared location between module instances.
  We need a single stack of active continuations, and a single bit that says
  if we are resuming - that should not change when we call into a module.
* When we resume, we use doCall, like CallRef does, to support cross-module
  calls.

self()->currContinuation is now generalized to use getCurrContinuation(),
which fetches it from the shared data. There is also a new
clearExecutionState() which is needed to wipe the stack after a trap etc.

With this, the large "scheduler" testcase can now run.

Author: kripken

src/tools/wasm-shell.cpp

@@ -232,6 +232,9 @@ struct Shell {
         WASM_UNREACHABLE("unexpected error");
       }
       if (flow.suspendTag) {
+        // This is an unhandled suspension. Handle it here - clear the
+        // suspension state - so nothing else is affected.
+        instance->clearContinuationStore();
         return SuspensionResult{};
       }
       return flow.values;