Implement new rule S8908 - @CacheResult methods

This rule detects methods annotated with @CacheResult that return void.
Since void methods have no return value to cache, applying @CacheResult
to them is meaningless and indicates a misunderstanding of how caching works.

Author: romainbrenguier

its/autoscan/src/test/java/org/sonar/java/it/AutoScanTest.java

@@ -199,7 +199,7 @@ public void javaCheckTestSources() throws Exception {
     softly.assertThat(newDiffs).containsExactlyInAnyOrderElementsOf(knownDiffs.values());
     softly.assertThat(newTotal).isEqualTo(knownTotal);
     softly.assertThat(rulesCausingFPs).hasSize(10);
-    softly.assertThat(rulesNotReporting).hasSize(19);
+    softly.assertThat(rulesNotReporting).hasSize(20);
 
     /**
      * 4. Check total number of differences (FPs + FNs)