RFR: 8335896: Source launcher should set TCCL

[Christian Stein]

Please review this change to set the context class loader of the current thread to the in-memory class loader when the `java` launcher is invoked in source mode. Having the source launcher set the TCCL to the in-memory classloader is benefical for scenarious depending on the TCCL being set to the application-loading loader.

For example, the single-argument taking [`ServiceLoader.load(Class)`](https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/ServiceLoader.html#load(java.lang.Class)) method creates "a new service loader for the given service type, using the current thread's [context class loader](https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/Thread.html#getContextClassLoader())."

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Commit messages:
 - JDK-8335896: Source launcher should set TCCL

Changes: https://git.openjdk.org/jdk/pull/20097/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20097&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335896
  Stats: 23 lines in 2 files changed: 22 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20097.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20097/head:pull/20097

PR: https://git.openjdk.org/jdk/pull/20097