NestingDepth (level 6)

Description

Let's start enabling it and set its max_depth to 6 on NestingDepth of the scss-lint static analysis as there are level 7 SCSS appeared in the current code (1aae91cf (2017-10-27)).

Proposal

In #23485 (moved), enabling NestingDepth with level 4 was suggested, but we are far away from that. At the starting point we should enable NestingDepth with max_depth: 6 right now. Then we won't have any more 7-nested SCSS code.

Links / references

/label ~"static analysis" ~"technical debt"

Edited by Takuya Noguchi