### Details:
- Introduce new low precision types `u2`, `u3`, `u6`.
- Introduce `ov::element::Iterator` for low precision types like `u1,
u2, u3, u4, i4, u6`:
- Gives pointer like access to low precision values in Tensor,
containers etc.
- Can be used by STL algorithms to access data in unified algorithms for
data manipulation.
- Can be used in Constant, Convert operators to replace duplicate
implementations for accessing low precision data (bin-size reduction).
- Can be used for operator reference implementation or plugin if there
is no hardware specific solution.
### Tickets:
- [CVS-126998](https://jira.devtools.intel.com/browse/CVS-126998)
- Part of
[CVS-128024](https://jira.devtools.intel.com/browse/CVS-128024)
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