Keep radix for integer literals in generated bindings

[miikkas]

The radices of integer literals in the input code, including both C and C++, are retained on a best-effort basis in the generated bindings.

• The radix of a C/C++ integer literal in constant, enum, or macro definition is parsed. If it can't be determined, the code falls back to not doing anything about the radix.
  • This can be currently optionally enabled with Builder (.keep_integer_radices(true)) or CLI (--keep-integer-radices) switches. For now, the default is to have the feature off.
• During Rust code generation, the radix of an integer literal – if it has been determined – is then used to output that integer's value represented in that number base.
• New testing is added in the form of unit tests for parsing the radix of a Clang CXToken_Literal token and for outputting the tokens during codegen, and also as a new test header file paired with its matching expected Rust binding output.
• Existing tests with hexadecimal or octal integers are updated to keep the corresponding radices of those values.

Resolves #3236.

[miikkas]

I have now included additional testing to the PR.

Regarding the 13 failing existing tests: It seems that the differences are due to bindgen now generating, as intended, Rust literals using hexadecimal representation, while the values themselves have correctly stayed the same. ~Should I fix the expected code accordingly?~

edit: I have adjusted the expected code accordingly.

[miikkas]

The test I added was changed to use C++14 instead of C23, as it seems that the latter is not available for clang 9.0, which IIUC is used in the CI.

I have changed the expected side of the previously failing existing tests. Those changes are currently included in a separate commit in case that makes review less cumbersome. ~I will squash it later as instructed in the contribution guidelines.~

edit: The commits have been squashed.

[miikkas]

I have made the solution a lot more robust and included further unit testing. In my view, this is ready for review.

r? @emilio @pvdrz

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[miikkas]

To mitigate possible churn and not force the feature on all users immediately, I've added an option defaulting to off as per https://github.com/rust-lang/rust-bindgen/issues/3236#issuecomment-3064790027.

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[miikkas]

The latest change removed the varying case long long suffixes (i.e. lL and Ll) from the INTEGER_SUFFIXES array, since those are not permitted by the C standard nor are they supported by clang or gcc. Additionally, I adjusted the length of some documentation rows that exceeded rustfmt's configured maximum of 80, and I added some testing for shorts and chars as well in the new .hpp test file.

[miikkas]

The commits have now been squashed into one commit that should stand on its own.