Add ability to read dataitem without advancing

[Odonno]

I have the need to read the current DataItem without advancing. What I want to do is:

1. Read the current data item and store it in a ReadOnlyMemory
2. Do not advance (or go back to the previous position)
3. Re-read the current data item but this time reading the semantic tag (and the value if needed)

[mcatanzariti]

Thank you for your contribution