Use Objects.equals instead of hand-rolled String == comparison (CodeQL java/reference-equality-on-strings)

[vharseko]

Summary

Resolves the single java/reference-equality-on-strings CodeQL alert in
Responses.java.

ResourceResponseImpl.equals() delegated to a private isEqual(String, String)
helper whose first line was a s1 == s2 reference comparison. The reference
check was an intentional fast-path (and both-null shortcut) with the real
value comparison delegated to s1.equals(s2) — so the code was correct, but:

• CodeQL flags the String == String, and
• the helper is a hand-rolled reimplementation of java.util.Objects.equals.

Fix

Replace the two isEqual(...) calls with Objects.equals(...) (already
imported) and delete the helper:

return Objects.equals(id, that.id) && Objects.equals(revision, that.revision);

Behaviour is identical — Objects.equals(a, b) performs the same
a == b || (a != null && a.equals(b)) null-safe comparison, including the
same reference fast-path and both-null handling.

Testing

mvn -o -pl commons/rest/json-resource -am compile — BUILD SUCCESS.