fix(java): avoid eqeq false positives on null checks

[0xTaoZ]

Summary

• exclude Java null comparisons from the eqeq self-comparison rule
• add a regression fixture for the ternary null-guard shape reported in False positive for java.lang.correctness.eqeq.eqeq #4019

Rationale

The rule is meant to report expressions like x == x or x != x. A ternary guard such as expr != null ? ... : ... is valid control flow and should not be reported as a self-comparison.

Fixes #4019.

Validation

• uvx semgrep --test --config java/lang/correctness/eqeq.yaml java/lang/correctness/eqeq.java
• uvx semgrep --validate --config java/lang/correctness/eqeq.yaml
• uvx semgrep --test --config java/lang/correctness java/lang/correctness
• git diff --check

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[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}