Function fxhash_32 

const fn fxhash_32(bytes: &[u8]) -> u32

Const function to compute the FxHash of a byte array.

FxHash is a speedy hash algorithm used within rustc. The algorithm is satisfactory for our use case since the strings being hashed originate from a trusted source (the ICU4X components), and the hashes are computed at compile time, so we can check for collisions.

We could have considered a SHA or other cryptographic hash function. However, we are using FxHash because:

1. There is precedent for this algorithm in Rust
2. The algorithm is easy to implement as a const function
3. The amount of code is small enough that we can reasonably keep the algorithm in-tree
4. FxHash is designed to output 32-bit or 64-bit values, whereas SHA outputs more bits, such that truncation would be required in order to fit into a u32, partially reducing the benefit of a cryptographically secure algorithm