feat: add trait_impl_reduntant_assoc_item diagnostic

[Young-Flash]

part of #15958, will try to add quickfix for the diagnostic if this PR is ok with you guys

[Young-Flash]

@rustbot ready

[Young-Flash]

@Veykril @lnicola could you help review this when you are free?

[Veykril]

Small nit but otherwise lgtm. We should definitely look into adding some more utility functions for creating better diagnostic text ranges for things (currently most assists still create the ranges in some random ways).

@bors delegate+

[bors]

✌️ @Young-Flash, you can now approve this pull request!

If @Veykril told you to "r=me" after making some further change, please make that change, then do @bors r=@Veykril

[Young-Flash]

@bors r=@Veykril

[bors]

📌 Commit fbe494a has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit fbe494a with merge 421a0a4...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing 421a0a4 to master...

[lnicola]

[saiintbrisson]

Hi! This feature introduced a bug when unwrapping this file_id:

rust-analyzer/crates/ide-diagnostics/src/handlers/trait_impl_redundant_assoc_item.rs

Line 47 in 932d85b

FileRange { file_id: d.file_id.file_id().unwrap(), range: diagnostic_range },

The function returns None if the file is a macro file:

rust-analyzer/crates/span/src/lib.rs

Lines 253 to 259 in 932d85b

	#[inline]
	pub fn file_id(self) -> Option<FileId> {
	match self.0 & Self::MACRO_FILE_TAG_MASK {
	0 => Some(FileId::from_raw(self.0)),
	_ => None,
	}
	}

Maybe changing it to something like trait_impl_missing_assoc_item will work?

rust-analyzer/crates/ide-diagnostics/src/handlers/trait_impl_missing_assoc_item.rs

Lines 23 to 31 in f532576

	Diagnostic::new(
	DiagnosticCode::RustcHardError("E0046"),
	format!("not all trait items implemented, missing: {missing}"),
	adjusted_display_range::<ast::Impl>(
	ctx,
	InFile { file_id: d.file_id, value: d.impl_.syntax_node_ptr() },
	&|impl_| impl_.trait_().map(|t| t.syntax().text_range()),
	),
	)