False positive cast diagnostics with DSTs and zerocopy

[ShoyuVanilla]

There's still a problem with KnownLayout when the DST is wrapped:

use zerocopy::KnownLayout;

#[derive(KnownLayout)]
#[repr(C)]
pub struct Dst([u8]);

#[derive(KnownLayout)]
#[repr(C)]
pub struct Struct {
    pub dst: Dst,
}

cannot cast thin pointer `*mut __ZerocopyKnownLayoutMaybeUninit` to fat pointer `*mut _` rust-analyzer[E0607]

rust-analyzer 1.85.1 (4eb16125 2025-03-15)

No problem with rustc.

Originally posted by @cloneable in #18682

[cloneable]

Thank you!