use non deprecated way to get record name

multiple locations [1] get record name using `._name` which is marked as deprecated [2]

we could have an utility function that uses the modern way and falls back to `_name` if not found to be backward compatible but allow future versions of immutable to drop `._name`.

[1] https://github.com/immutable-js/immutable-devtools/blob/3bd80e851f51a1b78a860c1e6e47c69e400b268f/packages/devtools/src/createFormatters.ts#L121

https://github.com/immutable-js/immutable-devtools/blob/3bd80e851f51a1b78a860c1e6e47c69e400b268f/packages/devtools/src/createFormatters.ts#L148

[2] https://github.com/immutable-js/immutable-js/blob/9acd11a87e1c628f08639f9ae0539073f4ee46d8/src/Record.js#L63

Start in packages/devtools/src/createFormatters.ts at the two cited locations that access `._name`, then compare the deprecated API reference in Record.js with the modern record-name API. Centralize the lookup with backward compatibility and verify that record formatting still obtains names without relying directly on the deprecated access.

Written by the indexing model from the issue text.