STYLE: variables: have separate token type

src/OpenFOAM/db/IOstreams/Sstreams/ISstream.C

src/OpenFOAM/db/IOstreams/token/token.H

src/OpenFOAM/db/IOstreams/token/tokenI.H

src/OpenFOAM/db/IOstreams/token/tokenIO.C

src/OpenFOAM/db/dictionary/primitiveEntry/primitiveEntryIO.C