Emit lint about redundant closure on the closure node itself

[samueltardieu]

Fixes #14789

changelog: [redundant_closure], [redundant_closure_for_method_calls]: allow lint to be allowed or expected on the closure expression itself

[rustbot]

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[samueltardieu]

r? clippy

[samueltardieu]

r? clippy

[samueltardieu]

Note: the change are trivial, and are best reviewed with "hide whitespace changes" option on, as using span_lint_hir_and_then() instead of span_lint_and_sugg() as added an indentation level but the content hasn't changed.

[y21]

r? @y21