Fix enableExtensionFunctions in Java 24+

[gjwatts]

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• If this PR fixes an Issue, the description includes "Fixes #FILLMEIN" or "Resolves #FILLMEIN" (verify release bug label if applicable: https://github.com/OpenLiberty/open-liberty/wiki/Open-Liberty-Conventions).
• If this PR resolves an external Known Issue (including APARS), the description includes "Fixes #FILLMEIN" or "Resolves #FILLMEIN".

Fixes #30526

In Java 24, the default value for jdk.xml.enableExtensionFunctions was changed from true to false (reference).
This broke our JUnit XML to HTML transformations for FAT output in the junit.html directory.
Forcing the jdk.xml.enableExtensionFunctions value back to true resolves this issue.

[gjwatts]

#build (view Open Liberty Personal Build - ❌ completed with errors/failures.)

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[LibbyBot]

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• 1 test infrastructure code files were changed.

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[gjwatts]

Only 1 FAT failed and it was an intermittent one. Kicking off Java 24 testing next.

[LibbyBot]

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