Make all VM sources pass clang-tidy checks

[mkustermann]

This is a tracking bug for ensuring all VM source pass clang-tidy checks.

Consider also adding more flags to the compiler:

• -Wconversion

[rmacnak-google]

See also #11526

[mkustermann]

Over time I think we can add more and more checks.

If there are fine grained flags for the compiler itself we should use them and otherwise we can use the clang-tidy linter.

(e.g. Some bugs have been introduced in the past due to uninitialized fields. Getting the compiler error on those can be done via -Weffc++ - though that enables a lot more than we actually want)