setting linter rules in analysis_options.yaml is confusing

[DetachHead]

Describe the issue
as far as i can tell, there are three different sections for linter rules:

• linter.rules
• analyzer.language
• analyzer.strong-mode

i think it would be much simpler if there was only one. currently it's confusing to new users as it's difficult to find the correct section or track down the documentation for individual rules - see #48553 (comment) and #48650

[srawlins]

We should also provide a schema at schemastore.org.

[bwilkerson]

The plan is for the analyzer.strong-mode section to be deprecated and eventually for support to be removed. It will be replaced by the analyzer.language section, but restructured slightly to be more consistent with the current language definition.

The reason for the analyzer.language section is that we originally thought of these checks as being a way to make the language's type system more sound. I think that was more accurate when we were experimenting with "strong mode" (which led to some of the changes added in Dart 2.0). We might well want to think about making these lints now rather than "language" modifiers.

I believe it's the case that these checks are all local now, and don't really impact the language semantics.