Avoid redundant filtering in FilteredMap.size()

Since keySet() already applies the filter, size() evaluated the
predicate twice for every accepted key.

This commit uses delegate.keySet() instead, avoiding the second
evaluation as well as a FilteredSet and FilteredIterator allocation.

Closes gh-37256

Signed-off-by: Hyunwoo Jung <hyunwoojung@kakao.com>

spring-core/src/main/java/org/springframework/util/FilteredMap.java

@@ -56,7 +56,7 @@ final class FilteredMap<K, V extends @Nullable Object> extends AbstractMap<K, V>
 	@Override
 	public int size() {
 		int size = 0;
-		for (K k : keySet()) {
+		for (K k : this.delegate.keySet()) {
 			if (this.filter.test(k)) {
 				size++;
 			}