Trivially-shareable constraint should be enforced for captured variables

[aam]

Variables captured in closures should be checked whether they have trivially-shareble content: this is continuation #60825.

Currently captured content is not checked allowing having tests like this to pass:

sdk/tests/ffi/isolate_group_shared_send_test.dart

Line 25 in 0730b31

rp.sendPort.send("hello");