Object-based checkpointing+eager support for mutable hash tables

Small eager execution fixes: omits op names, and sets a unique shared_name for each table by default to prevent automatic sharing (since there's no op name uniquification).

There are some TODOs about the shared_names, since eager execution's kernel caching will cache a new kernel for each shared_name. Only an issue if tables are created in a loop (and variables have the same issue; still on my list to fix that too).

PiperOrigin-RevId: 209445076