[clang][NFC] Rename stale TypeSourceInfo DI variables (#166082)
Fixes #165346
This patch renames stale variable names where `TypeSourceInfo` objects
were still using the old `DI` (`DeclaratorInfo`) naming convention.
Specifically, variables of type `TypeSourceInfo` have been updated from
`DI` to `TSI` to improve code clarity and maintain consistency with the
current naming.