Request for review: gh-129273 - `string.Formatter` handling attribute access for auto-numbered positional fields

This closes 4 replicate issues.
The PR is small and fixes this efficiently.

My latest issue: string.Formatter does not handle non-indexed item and attribute access · Issue #129273 · python/cpython · GitHub
PR: bpo-27307: string.Formatter unnumbered key/attributes by qm2k · Pull Request #21767 · python/cpython · GitHub

What does it do with string.Template?

Wrong name. It is string.Formatter, nothing to do with string.Template:man_facepalming: Fixed it, thanks.