[clang-tidy] Add user-defined functions to `bugprone-unsafe-functions` check (#106350)

Adds the check option `bugprone-unsafe-functions.CustomFunctions` to be
able to match user-defined functions a

[clang-tidy] Add user-defined functions to `bugprone-unsafe-functions` check (#106350)

Adds the check option `bugprone-unsafe-functions.CustomFunctions` to be
able to match user-defined functions as part of the checker.
Adds the option `bugprone-unsafe-functions.ReportDefaultFunctions` to
disable reporting the default set of functions as well.

The functions names are matched using the same mechanism as the
`matchesAnyListedName` tidy matcher, documented in
`unsafe-functions.rst`.

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