RFR: 8339332: Clean up the java launcher code

[Jaikiran Pai]

On Tue, 10 Sep 2024 06:15:57 GMT, Jaikiran Pai <jpai at openjdk.org> wrote:

> This was being done in the C code to support a long outdated "JRE selection" feature (mJRE https://bugs.openjdk.org/browse/JDK-8058407) which required it to parse the jar's manifest.

I would like to note here that the mJRE feature is currently still supported (only) in JDK 8. What that means is, the `java` launcher from JDK 8 will parse jar files being launched to see if they specify a specific JRE version (even latest mainline version of JDK is allowed) and if it finds one, then the Java 8's launcher is expected to correctly launch the specified JRE. With the change that has been done in this PR, I have manually verified that a Java 8 launcher will still be able to launch the latest mainline JRE (and thus the application), even after the changes in this current PR.

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PR Comment: https://git.openjdk.org/jdk/pull/20929#issuecomment-2345307704