### What changes were proposed in this pull request?
This PR aims to fix `CaseInsensitiveMap` to be deterministic for addition.
### Why are the changes needed?
```scala
import org.apache.spark.sql.catalyst.util.CaseInsensitiveMap
var m = CaseInsensitiveMap(Map.empty[String, String])
Seq(("paTh", "1"), ("PATH", "2"), ("Path", "3"), ("patH", "4"), ("path", "5")).foreach { kv =>
m = (m + kv).asInstanceOf[CaseInsensitiveMap[String]]
println(m.get("path"))
}
```
**BEFORE**
```
Some(1)
Some(2)
Some(3)
Some(4)
Some(1)
```
**AFTER**
```
Some(1)
Some(2)
Some(3)
Some(4)
Some(5)
```
### Does this PR introduce _any_ user-facing change?
Yes, but this is a bug fix on non-deterministic behavior.
### How was this patch tested?
Pass the newly added test case.
Closes#29172 from dongjoon-hyun/SPARK-32377.
Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
8c7d6f9733