Check for pointer validity when casting raw pointer to reference.

[celinval]

Requested feature: Kani should automatically check if a raw pointer is valid before any conversion to a reference, strengthening the verification of unsafe code.
Use case: This will help enable modular verification of safe abstractions. Kani detects invalid memory access only when the reference or dangling pointer is used.
Link to relevant documentation (Rust reference, Nomicon, RFC):

Test case:

struct Store<'a, const LEN: usize> {
    data: [&'a i128; LEN],
}

impl<'a, const LEN: usize> Store<'a, LEN> {
    pub fn from(var: &i64) -> Self {
        let ref1: *const i64 = var;
        let ref2: *const i128 = ref1 as *const i128;
        unsafe {
            Store { data: [&*ref2; LEN] }  // ---- THIS LINE SHOULD FAIL
        }
    }
}

#[cfg_attr(kani, kani::proof)]
#[cfg_attr(not(kani), test)]
pub fn check_store() {
    let val = 1;
    let broken = Store::<3>::from(&val);
    assert_eq!(broken.data.len(), 3)
}

Note: The harness above succeeds under playground run (version 1.75.0), and with Kani, but it correctly fails under MIRI.

[celinval]

I.e.: The pointer is not dangling and the allocation size is greater or equal to the reference type.