[core] Low precision element iterator and u2, u3, u6 types (#23279)

### 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)

cmake/developer_package/ncc_naming_style/openvino.style

@@ -18,7 +18,7 @@ VariableReference: '^\w+$'
 
 EnumName: '^[A-Z][\w]+$'
 # excepts element_type
-EnumConstantName: '^([A-Z\d_]+|undefined|dynamic|boolean|bf16|f16|f32|f64|i4|i8|i16|i32|i64|u1|u4|u8|u16|u32|u64|nf4|f8e4m3|f8e5m2|string|asymmetric|align_corners|round_prefer_floor|round_prefer_ceil|floor|ceil|simple|nearest|linear|linear_onnx|cubic|area|scales|sizes|half_pixel|tf_half_pixel_for_nn|pytorch_half_pixel|asymetric)$'
+EnumConstantName: '^([A-Z\d_]+|undefined|dynamic|boolean|bf16|f16|f32|f64|i4|i8|i16|i32|i64|u1|u2|u3|u4|u6|u8|u16|u32|u64|nf4|f8e4m3|f8e5m2|string|asymmetric|align_corners|round_prefer_floor|round_prefer_ceil|floor|ceil|simple|nearest|linear|linear_onnx|cubic|area|scales|sizes|half_pixel|tf_half_pixel_for_nn|pytorch_half_pixel|asymetric)$'
 # TODO: align
 UsingDeclaration: '^.*$'
 TypedefName: '^.*$'