Use clang-format to correct formatting to be in agreement with the [Google C++ Style Guide](https://google.github.io/styleguide/cppguide.html). Doing this simplifies the process of accepting changes. Also fixed a few warnings flagged by clang-tidy.

PiperOrigin-RevId: 246350737

ConsumeDecimalNumber has fairly non-trivial logic, and a previous
version has crashed inexplicably on Android. Having some test coverage
will make it easier to tweak / simplify the function later on.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=192821751