java: add «2185. Counting Words With a Given Prefix»

Refactor to stream.

URL:	https://leetcode.com/problems/counting-words-with-a-given-prefix/
Signed-off-by: Matej Focko <me@mfocko.xyz>

java/counting-words-with-a-given-prefix.java

@@ -1,13 +1,5 @@
 class Solution {
   public int prefixCount(String[] words, String pref) {
-    var count = 0;
-
-    for (var word : words) {
-      if (word.startsWith(pref)) {
-        ++count;
-      }
-    }
-
-    return count;
+    return (int) (Arrays.stream(words).filter(word -> word.startsWith(pref)).count());
   }
 }