[vm] Cache LanguageError result of metadata evaluation

Copying of pragmas during hot reload (Library::CopyPragmas) relies on
pragma metadata being fully evaluated in the earlier stage of hot reload
(in Library::EvaluatePragmas()).

However, if evaluation of metadata has ended with LanguageError,
the result of evaluation was not cached and metadata remains in
the unevaluated state, which triggers assertion in Library::CopyPragmas.

This change adds caching of the metadata evaluation result if
it ends with LanguageError.

TEST=ffi/abi_specific_int_incomplete_jit_test
Fixes #59665

Change-Id: I25e7b8f298f96ff4665e75fbbcbdb6b146c08f61
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/399200
Commit-Queue: Ryan Macnak <[email protected]>
Reviewed-by: Ryan Macnak <[email protected]>
Auto-Submit: Alexander Markov <[email protected]>

Author: alexmarkov

runtime/vm/object.cc

@@ -14207,7 +14207,7 @@ ObjectPtr Library::GetMetadata(const Object& declaration) const {
   }
   if (!value.IsSmi()) {
     // Metadata is already evaluated.
-    ASSERT(value.IsArray());
+    ASSERT(value.IsArray() || value.IsLanguageError());
     return value.ptr();
   }
   const auto& smi_value = Smi::Cast(value);
@@ -14218,7 +14218,8 @@ ObjectPtr Library::GetMetadata(const Object& declaration) const {
                 *this, kernel_offset,
                 /* is_annotations_offset = */ declaration.IsLibrary() ||
                     declaration.IsNamespace()));
-  if (evaluated_value.IsArray() || evaluated_value.IsNull()) {
+  if (evaluated_value.IsArray() || evaluated_value.IsNull() ||
+      evaluated_value.IsLanguageError()) {
     ASSERT(evaluated_value.ptr() != Object::empty_array().ptr());
     SafepointWriteRwLocker ml(thread, thread->isolate_group()->program_lock());
     MetadataMap map(metadata());