Fix Class.getMethod() to reject non-public interface methods

[tomal-majumder]

Fix Class.getMethod() to throw NoSuchMethodException for non-public interface methods

Problem

Class.getMethod() must return only public methods or throw NoSuchMethodException as per Java specification. Previously, when invoked on interface types with non-public methods (private static or non-static), the method incorrectly returned null instead of throwing the required exception.

Root Cause

The issue was in the initialResultShouldBeReplaced code path in getMethodHelper(). When publicOnly was true but the initial result was a non-public method, and no public alternatives were found, the method returned null instead of calling throwExceptionOrReturnNull().

Test cases added in Java9andUp/GetMethodTests covering cases of Class.getMethod() call for both public and non-public interface methods.

Test Results:

Local builds and Jenkins grinder tests were executed for aarch64 using JDK 11 and JDK 25.

• sanity.functional – PASS and stable
• extended.openjdk – PASS and stable
• sanity.openjdk – JDK11: fails on jdk_lang_j9_0 and jdk_lang_j9_1. JDK25 fails on java/util/StringJoiner/StringJoinerTest

The sanity.openjdk failures are already tracked issues:

• jdk_lang_j9_0 and jdk_lang_j9_1 failures observed across multiple Java levels (JDK 11, 17) and platforms (linux64, x86-64_mac): jdk_lang_j9_0 and jdk_lang_j9_1, Unexpected provider count. Expected: 13. Actual: 12 #23389
• StringJoinerTest OutOfMemoryError: Java heap space has recently been seen in openjdk25 on ppc64le_linux: OpenJDK java/util/StringJoiner/StringJoinerTest OutOfMemoryError: Java heap space #18708 (comment)

These failures are outside this change and appear to be existing issues.

Fixes: #22448

[babsingh]

Also, the commit guidelines are not followed: https://github.com/eclipse-openj9/openj9/blob/master/CONTRIBUTING.md#commit-guidelines -> The body should be wrapped at 72 characters.

[babsingh]

• Click "Resolve Conversation" for the feedback items that have already been addressed so the comments are collapsed.
• Once you have addressed the remaining feedback regarding test stabilization, run and verify the changes using a personal build.
• When everything is validated and ready for merge, set the PR status to "Ready to review".

[babsingh]

jenkins test sanity amac jdk21

[babsingh]

jenkins test sanity alinux64 jdk11

[babsingh]

Documenting PR build links so only minimal testing is required for the requested formatting changes:

• JDK11 alinux: https://openj9-jenkins.osuosl.org/job/PullRequest-OpenJ9/8796
• JDK21 amac: https://openj9-jenkins.osuosl.org/job/PullRequest-OpenJ9/8795

[babsingh]

jenkins test sanity.functional amac jdk17