Simplify how inline asm handles MaybeUninit

[WaffleLapkin]

This is just better, but this is also allows it to handle changes from #149614 (i.e. ManuallyDrop containing MaybeDangle).

[rustbot]

r? @jdonszelmann

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[taiki-e]

Could you also update the same code in rustc_codegen_cranelift?

rust/compiler/rustc_codegen_cranelift/src/inline_asm.rs

Lines 860 to 872 in eb171a2

	// Adapted from https://github.com/rust-lang/rust/blob/f3c66088610c1b80110297c2d9a8b5f9265b013f/compiler/rustc_hir_analysis/src/check/intrinsicck.rs#L136-L151
	ty::Adt(adt, args) if fx.tcx.is_lang_item(adt.did(), LangItem::MaybeUninit) => {
	let fields = &adt.non_enum_variant().fields;
	let ty = fields[FieldIdx::ONE].ty(fx.tcx, args);
	let ty::Adt(ty, args) = ty.kind() else {
	unreachable!("expected first field of `MaybeUninit` to be an ADT")
	};
	assert!(
	ty.is_manually_drop(),
	"expected first field of `MaybeUninit` to be `ManuallyDrop`"
	);
	let fields = &ty.non_enum_variant().fields;
	let ty = fields[FieldIdx::ZERO].ty(fx.tcx, args);

[rustbot]

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

[WaffleLapkin]

@taiki-e good catch, I've updated it too.