Ignore override of function in rule function-naming

[paul-dingemans]

Description

A function override should not be reported as the interface of class that defines the function might be out of scope of the project in which case the function name can not be changed. Note that the function will still be reported at the interface or class itself whenever that interface or class is defined inside the scope of the project.

Closes #2271

Checklist

Before submitting the PR, please check following (checks which are not relevant may be ignored):

• Commit message are well written. In addition to a short title, the commit message also explain why a change is made.
• At least one commit message contains a reference Closes #<xxx> or Fixes #<xxx> (replace<xxx> with issue number)
• Tests are added
• KtLint format has been applied on source code itself and violations are fixed
• CHANGELOG.md is updated
• PR description added

Documentation is updated. See difference between snapshot and release documentation

• Snapshot documentation in case documentation is to be released together with a code change
• Release documentation in case documentation is related to a released version of ktlint and has to be published as soon as the change is merged to master
• In case of adding a new rule, it needs to be added to experimental rules documentation