Create lint groups

[BD103]

See the project board for a definitive list, along with what lints go in what categories. As of writing this, the categories are:

• Correctness
• Suspicious
• Complexity
• Performance
• Style
• Restriction
• Nursery

(They're essentially the same as Clippy's lint groups!)

[BD103]

This can be done with LintStore::register_group(). This will probably require some additional metadata to live alongside Lint definitions, so we may need to define a custom declare_tool_lint! macro. See register_categories() for how Clippy does this.