wasm_sdk: non-halt topdown errors in host-builtins are 'undefined' (#3321)

Before, the consequence of a non-halt host-builtin error was that the entire
eval result was undefined.

Now, only the result of evaluating the builtin itself is undefined.

Fixes #3320.

Signed-off-by: Stephan Renatus <stephan.renatus@gmail.com>

test/cases/testdata/functionerrors/test-functionerrors-undefined-builtin-result.yaml

@@ -0,0 +1,12 @@
+cases:
+- data:
+  modules:
+  - |
+    package test
+    foo = units.parse_bytes("1KB")
+    bar = units.parse_bytes("foo") # undefined
+  note: functionerrors/undefined builtin result
+  query: data.test = x
+  want_result:
+  - x:
+      foo: 1000