JSTEP-6: rename `JsonLocation` as `TokenStreamLocation`

[cowtowncoder]

As part of JSTEP-6 -- Renaming of core entities for Jackson 3 -- there is desire to remove "Json" prefix from types that are not JSON-specific.
JsonLocation is such type, and seems better named as TokenStreamLocation (along with many other TokenStreamXxs types).
This is slightly intrusive but not extremely so.