Spell check action for markdown documentation (#8675)

Merge pull request 8675

.github/actions/spelling/README.md

@@ -0,0 +1,15 @@
+# check-spelling/check-spelling configuration
+
+File | Purpose | Format | Info
+-|-|-|-
+[dictionary.txt](dictionary.txt) | Replacement dictionary (creating this file will override the default dictionary) | one word per line | [dictionary](https://github.com/check-spelling/check-spelling/wiki/Configuration#dictionary)
+[allow.txt](allow.txt) | Add words to the dictionary | one word per line (only letters and `'`s allowed) | [allow](https://github.com/check-spelling/check-spelling/wiki/Configuration#allow)
+[reject.txt](reject.txt) | Remove words from the dictionary (after allow) | grep pattern matching whole dictionary words | [reject](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-reject)
+[excludes.txt](excludes.txt) | Files to ignore entirely | perl regular expression | [excludes](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-excludes)
+[only.txt](only.txt) | Only check matching files (applied after excludes) | perl regular expression | [only](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-only)
+[patterns.txt](patterns.txt) | Patterns to ignore from checked lines | perl regular expression (order matters, first match wins) | [patterns](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-patterns)
+[expect.txt](expect.txt) | Expected words that aren't in the dictionary | one word per line (sorted, alphabetically) | [expect](https://github.com/check-spelling/check-spelling/wiki/Configuration#expect)
+[advice.txt](advice.txt) | Supplement for GitHub comment when unrecognized words are found | GitHub Markdown | [advice](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-advice)
+
+Note: you can replace any of these files with a directory by the same name (minus the suffix)
+and then include multiple files inside that directory (with that suffix) to merge multiple files together.

.github/actions/spelling/advice.md

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+<!-- See https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-advice --> <!-- markdownlint-disable MD033 MD041 -->
+<details><summary>If you see a bunch of garbage</summary>
+
+If it relates to a ...
+<details><summary>well-formed pattern</summary>
+
+See if there's a [pattern](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples:-patterns) that would match it.
+
+If not, try writing one and adding it to the `patterns.txt` file.
+
+Patterns are Perl 5 Regular Expressions - you can [test](
+https://www.regexplanet.com/advanced/perl/) yours before committing to verify it will match your lines.
+
+Note that patterns can't match multiline strings.
+</details>
+<details><summary>binary-ish string</summary>
+
+Please add a file path to the `excludes.txt` file instead of just accepting the garbage.
+
+File paths are Perl 5 Regular Expressions - you can [test](
+https://www.regexplanet.com/advanced/perl/) yours before committing to verify it will match your files.
+
+`^` refers to the file's path from the root of the repository, so `^README\.md$` would exclude [README.md](
+../tree/HEAD/README.md) (on whichever branch you're using).
+</details>
+
+</details>

.github/actions/spelling/excludes.txt

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+# See https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples:-excludes
+(?:^|/)(?i)COPYRIGHT
+(?:^|/)(?i)LICEN[CS]E
+(?:^|/)package(?:-lock|)\.json$
+(?:^|/)vendor/
+/fonts/
+ignore$
+\.avi$
+\.eot$
+\.ico$
+\.jpe?g$
+\.lock$
+\.map$
+\.min\.
+\.mod$
+\.mp[34]$
+\.png$
+\.svg$
+\.ttf$
+\.wav$
+\.woff$
+\.woff2$
+^docs/pages/redirects/github\.html$
+^lib/jekyll/mime\.types$
+^lib/theme_template/example/index\.html$
+^lib/theme_template/example/_post\.md$
+^test/fixtures/empty_permalink\.erb$
+^test/fixtures/webrick/bar/baz\.html$
+^test/fixtures/webrick/bar/foo\.xhtml$
+^test/source/_posts/2009-06-22-no-yaml\.markdown$
+^\.github/