Define a standardized header ordering for Azure SDK for C++

[LarryOsterman]

Define a standardized header layout for the Azure SDK for C++.

This pull request defines a standardized convention for headers in the C++ repo.

In the C++ repo, headers will be grouped according to the following scheme:

For the C++ SDK, I propose we define the following ordering:

• P0: Main header.
• P1: Azure headers from the current package (headers starting with ‘”’)..
• P2: Azure headers from other packages
• P3: Headers starting with azure (specifically headers from azure_uamqp_c and azure_c_shared_utility)
• P4: C++ headers (‘<’ alphanumeric characters ‘>’)
• P4: C headers (‘<’ alphanumeric characters ‘.h>) (note: same priority as C++ so they will be grouped together).

There are also some special cases defined to handle header ordering conflicts (windows.h needs to go before other headers, get_env.hpp needs to go before all other headers, there are several uAMQP headers that need to be reordered).

Note that There is essentially NO source code changes associated with this pull request, the only new code changes are in the .clang-format file. All the other changes are a consequence of re-running clang-format on the repo.

Pull Request Checklist

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• C++ Guidelines
• Doxygen docs
• Unit tests
• No unwanted commits/changes
• Descriptive title/description
  • PR is single purpose
  • Related issue listed
• Comments in source
• No typos
• Update changelog
• Not work-in-progress
• External references or docs updated
• Self review of PR done
• Any breaking changes?

[antkmsft]

❤️ it is pretty cool what you've done with regexes, I didn't know it was possible.
Even if we find the order is not right somewhere (but I just looked and it looks right to me) - we have a way to fix it in the clang-format file.