Inconsistency between comments and code implementation

[YichiZhang0613]

I noticed a possible panic due to inconsistency between comments and code implementation in arrow-rs/arrow-array/src/array/union_array.rs. The details can be found in the following code.
I think this function should check whether index is out of bounds as your comment read before it is used as self.type_ids[index], which could avoid unnecessary panic.

   /// # Panics
    ///
    /// Panics if `index` is greater than the length of the array.
    pub fn type_id(&self, index: usize) -> i8 {
        self.type_ids[index]
    }

By the way, I think it would be more complete if the comment is modified to Panics if index is greater than or equal to the length of the array. instead of Panics if index is greater than the length of the array.

    /// # Panics
    ///
    /// Panics if `index` is greater than the length of the array.
    pub fn value_offset(&self, index: usize) -> usize {
        assert!(index < self.len());

[tustvold]

label_issue.py automatically added labels {'arrow'} from #5456