DebugInfo/Symbolize: Don't differentiate function/data symbolization

Before d08bd13a, only `SymbolRef::ST_Function`
symbols were used for .symtab symbolization. That commit added a `"DATA"` mode
to llvm-symbolizer which used `SymbolRef::ST_Data` symbols for symbolization.

Since function and data symbols have different addresses, we don't need to
differentiate the two modes. This patches unifies the two modes to simplify
code.

`"DATA"` is used by `compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_libcdep.cpp`.
`check-hwasan` and `check-tsan` have runtime tests.

Differential Revision: https://reviews.llvm.org/D96322