[clang] [clang-tools-extra] [llvm] [ADT] Refactor StringMap iterators (NFC) (PR #156137)

[Kazu Hirata via llvm-commits]

kazutakahirata wrote:

> Do we have dedicated unit tests for these iterators?

I wouldn't say `llvm/unittests/ADT/StringMapTest.cpp` is dedicated to iterators only, but it covers:

- the empty map
- the single-element map
- `for` loop over the map
- `erase(iterator)`
- `insert` return value
- ` keys()`

I'd say this is pretty good coverage.


https://github.com/llvm/llvm-project/pull/156137