[linter proposal] member function can be static

[stephane-archer]

class foo {
    String hello = "Hello World";
    ....
    void _bar(string s) {
        print(s)
    }
}

_bar does not use any member function so it can be static so it can be used by static and non-static function

[srawlins]

I'm deduplicating this to your earlier request: #57108