Request: read file position and value length of a tag without also reading the actual value

[bersbersbers]

Is your feature request related to a problem? Please describe.
I am unable to read the file position and value length of a tag without also reading the actual value. See an example code at https://stackoverflow.com/q/76897860/880783.

Describe the solution you'd like
I am looking for a way to access _dict[tag].value_tell and _dict[tag].length through a public API - namely, without acessing/decoding the data. Extending get_item to allow that would be one solution, as would be adding another getter method.

[darcymason]

Looking at the code, I think Dataset.get_item could be extended with a keep_deferred argument (default False). We would just need the documentation very clear that the caller would get a None value if it was a deferred-read element.