Add sanitize-inline-keyword check

Emits a warning if the "inline" keyword is set on the definition but not the declaration of a member method in an exported class.

This check sets Option_CanIgnoreIncludes; it's useful when using it with clazy-standalone to avoid having duplicate fixes (which may end up adding the inline keyword more than once to the same method).

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--ignore-included-files only works if the check has Option_CanIgnoreIncludes set. I was running in circles because the option didn't seem to have any effect, before I realised it has to be set in the Options parameter when constructing CheckBase in the check's constructor initializer list.

Also add a note to ClazyOption_IgnoreIncludedFiles docs.