[dwarfdump][NFC] Consistent printing of address ranges

This implement the insertion operator for DWARF address ranges so they
are consistently printed as [LowPC, HighPC).

While a dump method might have felt more consistent, it is used
exclusively for printing error messages in the verifier and never used
for actual dumping. Hence this approach is more intuitive and creates
less clutter at the call sites.

Differential revision: https://reviews.llvm.org/D38395

llvm-svn: 314523