Use codespell for spell-checking

[Piedone]

Is your feature request related to a problem?

There are typos in the source code. This is not a huge deal, but annoying and messy if it's just executable code, but a bigger issue if it's also in UI strings or documentation, something that a larger amount of people read.

Describe the solution you'd like

Add codespell for spell-checking as a PR check, i.e. in a GitHub Actions workflow. Codespell checks for known misspellings, so unlike spell-checkers that are meant for prose, it works really well for code, with a low false positive rate.

We at Lombiq have been test codespell in parallel with a traditional spell-checker (which we've used for about two years) for the last month, and it works really well. (You can see a run of it here: it runs in about 10s for a codebase of ~60k LOC, including installing it. So, it wouldn't delay the checks of a PR.

I'd use the codespell workflow from Lombiq GitHub Actions, which runs the codespell CLI and is trivial to use. We introduced it to Orchard Core Commerce too: OrchardCMS/OrchardCore.Commerce#520.

Describe alternatives you've considered

Either not using spell-checking or using a more traditional one. However, based on our experiences at Lombiq, I'd advise against either.

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