minor: Don't show layout info when hovering on locals

[Wilfred]

This is useful when the cursor is on the type name, but layout information tends to distract when the cursor is just on a local variable of that type.

Fixes #17096

[Veykril]

That doesn't address the issue. I like the layout info on locals a lot in fact as it is the easiest way to check the size of some arbitrary instantiated type.

As that linked issue states, Hover should only show type layout when hovering the definition, not a reference. This just removes hovers for locals though which is something completely different.

[Veykril]

To add to this, we should differentiate here

rust-analyzer/crates/ide/src/hover.rs

Lines 224 to 238 in cbcb977

	match IdentClass::classify_node(sema, &node)? {
	// It's better for us to fall back to the keyword hover here,
	// rendering poll is very confusing
	IdentClass::Operator(OperatorClass::Await(_)) => None,
	IdentClass::NameRefClass(NameRefClass::ExternCrateShorthand {
	decl,
	..
	}) => Some(vec![(Definition::ExternCrateDecl(decl), None, node)]),
	class => Some(
	multizip((class.definitions(), iter::repeat(None), iter::repeat(node)))
	.collect::<Vec<_>>(),
	),
	}

If we deal with a IdentClass::NameClass we should render the layout info, otherwise we should omit it