Clean-up used_underscore_*

[Jarcho]

This primarily reorders things to do cheaper checks before more expensive checks, but there are also some smaller changes:

• No macros are linted instead of only skipping external macros.
• expect and allow on the item in used_underscore_items now work. used_undercore_bindings already did this.
• is_used now more closely matches what unused_variables does. It takes very little for a variable to count as used.
• consts/statics and all type relative paths are checked
• Functions are linted if they're named, not just if they're called.

changelog: [used_underscore_bindings]: lint more cases where the binding is used
changelog: [used_underscore_items]: additionally check for allow end expect attributes on the item definition.

[rustbot]

r? @llogiq

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[github-actions]

Lintcheck changes for 8082081

Lint	Added	Removed	Changed
clippy::used_underscore_items	154	0	36

This comment will be updated if you push new changes

[llogiq]

Can you add some tests to show the modified behavior re consts/statics etc.?