Fixed: Fix some bugs SpotBugs reports (OFBIZ-12386)

After updating SpotBugs plugin to 4.8.6.r202406180231-6cf7b2c
in Eclipse 2023-03 (4.27.0) it reported:

<<Bug: Class (org.apache.ofbiz.webapp.WebAppCache) using singleton design pattern
has non-private constructor.

This class is using singleton design pattern and has non-private constructor
(please note that a default constructor might exist which is not private).
Given that, it is possible to create a copy of the object, thus violating the
singleton pattern.  The easier solution would be making the constructor private.
>>

As it's also used by WebAppCacheTest class I made it package. That's safer but
not enough so I also put it in exclude.xml
Also Chekstyle wants it to be final

framework/webapp/src/main/java/org/apache/ofbiz/webapp/WebAppCache.java

@@ -45,7 +45,7 @@
  *
  * @see <a href="https://en.wikipedia.org/wiki/Memoization">Memoization</a>
  */
-public class WebAppCache {
+public final class WebAppCache {
     // Synchronized map storing web applications.
     // The LinkedHashMap is used to maintain insertion order (which client code depends on).
     // There is no concurrent implementation of LinkedHashMap, so we are using manual synchronization instead.
@@ -57,7 +57,7 @@ public class WebAppCache {
      * Constructs an empty web application cache.
      * @param supplier the source from which components configurations are retrieved
      */
-    public WebAppCache(Supplier<Collection<ComponentConfig>> supplier) {
+    WebAppCache(Supplier<Collection<ComponentConfig>> supplier) {
         ccs = supplier;
         serverWebApps = new LinkedHashMap<>();
     }

spotbugs/exclude.xml

@@ -192,4 +192,10 @@ under the License.
     <Method name="equals" />
     <Bug pattern="EQ_CHECK_FOR_OPERAND_NOT_COMPATIBLE_WITH_THIS" />
   </Match><!-- ^ ^ not a problem, false positives -->
+  <Match>
+    <!-- As it's also used by WebAppCacheTest class I made it package. That's safer but not enough so it's also here -->
+    <Class name="org.apache.ofbiz.webapp.WebAppCache" />
+    <Method name="WebAppCache" />
+    <Bug pattern="SING_SINGLETON_HAS_NONPRIVATE_CONSTRUCTOR " />
+  </Match>
 </FindBugsFilter>