This is a big CL; no code is really "changed." We basically move 3
components into the public API, which can all be reviewed concisely
in the `api.txt` file.
* The AnalysisRule classes: `AbstractAnalysisRule` (which is good to
make public as a lot of the public API is specified and documented
here), `AnalysisRule`, `MultiAnalysisRule`.
* The Pubspec classes, available for linting pubspec files:
`PubspecDependency`, `PubspecDependencyList`, `PubspecEntry`,
`PubspecEnvironment`, `PubspecGitRepo`, `PubspecHost`, `PubspecNode`,
`PubspecNodeList`, `PubspecVisitor`.
* The `RuleVisitorRegistry` class. This class is needed by analysis
rule authors, and is part of the public API of AnalysisRule.
Change-Id: Ib1803180de9469f4ff39cf1778f96787f5f74b14
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/432363
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Sam Rawlins