Lint for bit shifts by a possibly negative value

What it does

The behavior of bit shifts by negative numbers is highly unintuitive as they are masking so you have 3u32 << -1 ⇒ 3u32 << (-1 & 0b11111) ⇒ 3u32 << 31 ⇒ 4294967295 instead of the likely expected behavior that when the shift is negative, it simply goes in the opposite direction.

Example

fn inverse_product_log2(y: i32) -> i32 {
    y << y
}

Was probably meant to be

fn inverse_product_log2(y: i32) -> i32 {
    if y < 0 {
        y >> -y
    } else 
        y << y
    }
}

Additional Context

the product logarithm for a base b is the inverse of the function x * bᕽ over x, so the inverse of the product log itself is x * bᕽ.

No implementation files or tests are named. Start by locating existing Rust Clippy lints and tests for shift operations, then compare their structure with the requested case. Done means the lint reliably identifies shifts by possibly negative values and has coverage for the example and expected diagnostic behavior.