Start uplifting clippy::for_loops_over_fallibles

I refactored the code:
- Removed handling of methods, as it felt entirely unnecessary
- Removed clippy utils (obviously...)
- Used some shiny compiler features
  (let-else is very handy for lints 👀)
- I also renamed the lint to `for_loop_over_fallibles` (note: no `s`).
  I'm not sure what's the naming convention here, so maybe I'm wrong.

compiler/rustc_lint/src/lib.rs

@@ -52,6 +52,7 @@ mod early;
 mod enum_intrinsics_non_enums;
 mod errors;
 mod expect;
+mod for_loop_over_fallibles;
 pub mod hidden_unicode_codepoints;
 mod internal;
 mod late;
@@ -86,6 +87,7 @@ use rustc_span::Span;
 use array_into_iter::ArrayIntoIter;
 use builtin::*;
 use enum_intrinsics_non_enums::EnumIntrinsicsNonEnums;
+use for_loop_over_fallibles::*;
 use hidden_unicode_codepoints::*;
 use internal::*;
 use let_underscore::*;
@@ -188,6 +190,7 @@ macro_rules! late_lint_mod_passes {
         $macro!(
             $args,
             [
+                ForLoopOverFallibles: ForLoopOverFallibles,
                 HardwiredLints: HardwiredLints,
                 ImproperCTypesDeclarations: ImproperCTypesDeclarations,
                 ImproperCTypesDefinitions: ImproperCTypesDefinitions,