rust: pin-init: internal: pin_data: self-referential drop order checks

Check drop order to ensure that usage of lifetime inside self-referential
struct is consistent with the order that the fields will dropped in drop
glue.

First, fields are checked according to their index to ensure that if `a`
borrows from `b`, `b` must outlive `a`. This is simple and produces a very
good diagnostic when misused.

Lifetime bounds can also be indirectly crafted with implied bounds that
make fields well-formed. For example, in this struct

    struct Foo {
        x: &'b &'a (),
        a: String,
        y: PrintOnDrop<&'b str>,
        b: String,
    }

`&'b &'a ()` will imply that `a` outlive `b`, which is inconsistent with
the actual drop order. For this case, create a `__drop_order_check`
function with field lifetimes and outlive relationship of them as generic
parameter, and ask Rust to prove that the types are well-formed inside the
generated function, to ensure that the bad implied bounds cannot happen.

The `__drop_order_check` also need to correlate lifetimes or types captured
by generics and the field lifetimes. Do this by inserting outlive bounds
when a field mentions a specific type or lifetime parameter.

Acked-by: Benno Lossin <lossin@kernel.org>
Link: https://patch.msgid.link/20261008-dev-selfref-v2-6-e280b3c8fba5@garyguo.net/
Signed-off-by: Gary Guo <gary@garyguo.net>

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