[Tracking issue] Rearrange location of some of the existing lints

Currently, the lint rules grouped as "methods" reside in clippy_lints/src/methods as there are a number of rules belonging to the "methods" group.
However, although the other groups such as "loops", "types", "transmute" and "misc" also have many relavent rules, they reside not in clippy_lints/src/<group_name> but in clippy_lints/src.
It would be great to have these groups located under <group_name> directory just like "methods". So I open this issue to do this refactoring and to keep track of it.

• loops (done by @nahuakang & @Y-Nak #6824)
• types (done by @Y-Nak #6724)
• transmute (done by @magurotuna #6716)
• functions (done by @Y-Nak #6990)
• methods (also needs to be refactored because currently most of rule implementation are included in clippy_lints/src/methods/mod.rs. Would be good if the implementations went to clippy_lints/src/methods/<lint_name>.rs.) (done by @TaKO8Ki #6886)
• misc (instead of creating a new directory named misc, split the lints one by one, and move them into where they fit most. )
• misc_early (same as misc) (in progress by @TaKO8Ki #7166, #7208)
• matches (in progress by @Y-Nak)

How to rearrange is like the following, proposed by @flip1995 on zulip

I would keep the declare_clippy_lint! in the mod.rs Best case would be that mod.rs only contains the lint definitions and the LintPass impl. Utility functions of the module should probably go in methods/utils.rs and then reexported for the module in mod.rs.

proposed by @camsteffen:

For each lint, create a new module at clippy_lints/src/<group_name>/<lint_name>.rs. Within that module, add a function fn check(cx, ..) (with any needed arguments) and move the implementation there.

CC @nahuakang @camsteffen

Start by reading the existing layout under clippy_lints/src, especially methods/mod.rs and the remaining misc, misc_early, and matches lint modules. Review the linked work in #7166, #7208, and the in-progress matches effort before choosing an unclaimed portion. Done means the selected lint implementations are arranged in appropriate modules while declarations and LintPass integration remain correct.