Optimizing queries for optional VM functions. (#17823)

Queries with IMPORT_OPTIONAL bypass reporting and full status creation
as a way to avoid generating a bunch of stack traces for cases where the
caller can gracefully handle the absence of an import. This change adds
EXPORT_OPTIONAL to provide the same functionality to callers that know
the export may not exist. This speeds up startup (when __init is omitted
on a module), shutdown (when __deinit is omitted on a module), and event
notification (__notify).
diff --git a/runtime/bindings/python/vm.cc b/runtime/bindings/python/vm.cc
index f8b758c..0be8912 100644
--- a/runtime/bindings/python/vm.cc
+++ b/runtime/bindings/python/vm.cc
@@ -819,6 +819,7 @@
       .value("IMPORT", IREE_VM_FUNCTION_LINKAGE_IMPORT)
       .value("IMPORT_OPTIONAL", IREE_VM_FUNCTION_LINKAGE_IMPORT_OPTIONAL)
       .value("EXPORT", IREE_VM_FUNCTION_LINKAGE_EXPORT)
+      .value("EXPORT_OPTIONAL", IREE_VM_FUNCTION_LINKAGE_EXPORT_OPTIONAL)
       .export_values();
 
   auto vm_buffer = py::class_<VmBuffer>(m, "VmBuffer");