Rollup merge of #145153 - joshtriplett:macro-kinds-plural, r=petrochenkov

Handle macros with multiple kinds, and improve errors

(I recommend reviewing this commit-by-commit.)

Switch to a bitflags `MacroKinds` to support macros with more than one kind

Review everything that uses `MacroKind`, and switch anything that could refer to more than one kind to use `MacroKinds`.

Add a new `SyntaxExtensionKind::MacroRules` for `macro_rules!` macros, using the concrete `MacroRulesMacroExpander` type, and have it track which kinds it can handle. Eliminate the separate optional `attr_ext`, now that a `SyntaxExtension` can handle multiple macro kinds.

This also avoids the need to downcast when calling methods on `MacroRulesMacroExpander`, such as `get_unused_rule`.

Integrate macro kind checking into name resolution's `sub_namespace_match`, so that we only find a macro if it's the right type, and eliminate the special-case hack for attributes.

This allows detecting and report macro kind mismatches early, and more precisely, improving various error messages. In particular, this eliminates the case in `failed_to_match_macro` to check for a function-like invocation of a macro with no function-like rules.

Instead, macro kind mismatches now result in an unresolved macro, and we detect this case in `unresolved_macro_suggestions`, which now carefully distinguishes between a kind mismatch and other errors.

This also handles cases of forward-referenced attributes and cyclic attributes.

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In this PR, I've minimally fixed up `rustdoc` so that it compiles and passes tests. This is just the minimal necessary fixes to handle the switch to `MacroKinds`, and it only works for macros that don't actually have multiple kinds. This will panic (with a `todo!`) if it encounters a macro with multiple kinds.

rustdoc needs further fixes to handle macros with multiple kinds, and to handle attributes and derive macros that aren't proc macros. I'd appreciate some help from a rustdoc expert on that.

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r? ````````@petrochenkov````````

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