Document which rules provide suggestions and improve consistency of rule autofixer notices

[bmish]

This is a documentation PR touching two areas.

Suggestions

The lightbulb 💡 emoji is the convention for denoting rules that provide editor suggestions. It's used by the official ESLint website as well as in the documentation of many popular ESLint plugins. Examples (note: I am a maintainer on some of these plugins and have been working to standardize the lists of rules):

• https://eslint.org/docs/latest/rules/
• https://github.com/sindresorhus/eslint-plugin-unicorn#rules
• https://github.com/ember-cli/eslint-plugin-ember#-rules
• https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin#rules
• https://typescript-eslint.io/rules/

My change adds this indicator to the README and as a notice in rule documentation files.

Currently, only one of our rules is auto-suggestable, but this change will help improve discovery of the relatively-new auto-suggestion feature, especially as more rules implement one.

Autofixers

While adding tests that this suggestion notice is properly present in the rule documentation file of any suggestable rules, I also added a test that the autofixer notice is present for fixable rules. In doing this, I standardized the fixable/suggestion notices at the top of the rule docs with the corresponding emojis, and added the fixable notice to many rule docs that were missing it.

[codecov]

Codecov Report

Merging #3359 (6b778c3) into master (8306a7b) will not change coverage.
The diff coverage is n/a.

❗ Current head 6b778c3 differs from pull request most recent head bb999c2. Consider uploading reports for the commit bb999c2 to get more accurate results

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  Files         123      123           
  Lines        8873     8873           
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  Hits         8655     8655           
  Misses        218      218           

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[ljharb]

Looks great overall!