Export ReverseSliceInPlace and ReverseSlice

... and add tests.

Test: TestReverseSliceInPlace, TestReverseSlice
Change-Id: I70f811207fdb2af891f7ef3fe19cbe5c7276135a

android/util.go

@@ -338,15 +338,19 @@ func firstUniqueMap[T comparable](in []T) []T {
 	return in[0:writeIndex]
 }
 
-// reverseSliceInPlace reverses the elements of a slice in place.
-func reverseSliceInPlace[T any](in []T) {
+// ReverseSliceInPlace reverses the elements of a slice in place and returns it.
+func ReverseSliceInPlace[T any](in []T) []T {
 	for i, j := 0, len(in)-1; i < j; i, j = i+1, j-1 {
 		in[i], in[j] = in[j], in[i]
 	}
+	return in
 }
 
-// reverseSlice returns a copy of a slice in reverse order.
-func reverseSlice[T any](in []T) []T {
+// ReverseSlice returns a copy of a slice in reverse order.
+func ReverseSlice[T any](in []T) []T {
+	if in == nil {
+		return in
+	}
 	out := make([]T, len(in))
 	for i := 0; i < len(in); i++ {
 		out[i] = in[len(in)-1-i]