message: Make StarlarkStr::get_hash public
  Summary: Used in the following diff
diff: @@ -134,7 +134,7 @@ impl StarlarkStr {
  }
  }
  - pub(crate) fn get_hash(&self) -> StarlarkHashValue {
  + pub fn get_hash(&self) -> StarlarkHashValue {
  // Note relaxed load and store are practically non-locking memory operations.
  let hash = self.str.hash.load(atomic::Ordering::Relaxed);
  if hash != 0 {
  