Java: update qhelp and add 'performace' tag

Author: Jami Cogswell

java/ql/src/Violations of Best Practice/Undesirable Calls/DoNotCallFinalize.md

@@ -1,6 +1,6 @@
 ## Overview
 
-Calling `finalize()` in application code may cause inconsistent program state or unpredicatable behavior.
+Triggering garbage collection by directly calling `finalize()` may either have no effect or may trigger unnecessary garbage collection, leading to erratic behavior, performance issues, or deadlock.
 
 ## Recommendation
 
@@ -23,5 +23,6 @@ This rule is focused on the use of existing `finalize()` invocations rather than
 
 ## References
 
-- Carnegie Mellon University, SEI CERT Oracle Coding Standard for Java: [MET12-J. Do not use finalizers](https://wiki.sei.cmu.edu/confluence/display/java/MET12-J.+Do+not+use+finalizers).
+- SEI CERT Oracle Coding Standard for Java: [MET12-J. Do not use finalizers](https://wiki.sei.cmu.edu/confluence/display/java/MET12-J.+Do+not+use+finalizers).
+- Java API Specification: [Object.finalize()](https://docs.oracle.com/javase/10/docs/api/java/lang/Object.html#finalize()).
 - Common Weakness Enumeration: [CWE-586](https://cwe.mitre.org/data/definitions/586).

java/ql/src/Violations of Best Practice/Undesirable Calls/DoNotCallFinalize.ql

@@ -9,6 +9,7 @@
  * @problem.severity error
  * @tags quality
  *       correctness
+ *       performance
  *       external/cwe/cwe-586
  */