feat: update max-depth for class static blocks

[mdjermanovic]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[x] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

Refs #15016, fixes max-depth.

What changes did you make? (Give an overview)

Updated the max-depth rule to treat class static blocks as separate contexts when calculating depth.

Before this change:

/* eslint max-depth: ["error", 2] */

function foo() {
    if (true) { // 1, ok
        class C {
            static { // does not count as a nested block, but it's still the same context
                if (true) { // 2, ok
                    if (true) { // 3, report as depth 3
                        if (true) { // 4, report as depth 4
                        }
                    }
                }
            }
        }
    }
}

After this change:

/* eslint max-depth: ["error", 2] */

function foo() {
    if (true) { // 1, ok
        class C {
            static { // separate context
                if (true) { // 1, ok
                    if (true) { // 2, ok
                        if (true) { // 3, report as depth 3
                        }
                    }
                }
            }
        }
    }
}

Is there anything you'd like reviewers to focus on?

This is somewhat similar to #15315, but unlike max-statements this rule does not report functions. It reports blocks that are nested too deeply, relative to something (program, or function body). I think it makes sense to report blocks inside static blocks, and to calculate depth relative to the top level of static blocks.

[btmills]

LGTM. I agree resetting depth in static blocks makes sense.