feat: lints for enum-name and constructor-name repetition

[ivov]

Adds two diagnostics that flag a name repeating the type it is already qualified by.

  [info] Variant names repeat the enum name
   ╭─[test.lis:2:6]
 1 │ 
 2 │ enum Color { ColorRed, ColorGreen }
   ·      ──┬──
   ·        ╰── each variant repeats this name
 3 │ 
   ╰────
  help: Drop the `Color` prefix from each variant (`ColorRed` to `Red`). A variant is already written as `Color.Red`, so the prefix repeats the enum name · code: [lint.enum_variant_names]

  [info] Constructor named after its type
   ╭─[test.lis:5:6]
 4 │ impl Point {
 5 │   fn point(x: int) -> Point {
   ·      ──┬──
   ·        ╰── repeats the type name
 6 │     Point { x }
   ╰────
  help: Calling this as `Point.point()` repeats the type name. Rename it to `new`, the conventional constructor name · code: [lint.self_named_constructors]