Collections module reformatting and minor code refactoring

[rhettinger]

• Code clean-up only. Overall logic and performance are unchanged.
• Use f-strings instead of format() calls.
• Use modern, zero-argument form of super()
• Simplify Counter.__repr__ logic to take advantage of order preserving dicts.
• Avoid duplicating the map slicing logic already present in copy().
• Switch direction of if-test to match the style in the rest of the module.

[miss-islington]

Thanks @rhettinger for the PR 🌮🎉.. I'm working now to backport this PR to: 3.9.
🐍🍒⛏🤖

[bedevere-bot]

GH-20798 is a backport of this pull request to the 3.9 branch.