RFR: 8333131: Source launcher should work with service loader SPI

[Christian Stein]

Please review this fix for the memory class loader to find classes defined by a modular source program; including classes referenced in its module descriptor.

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Commit messages:
 - 8333131: Source launcher should work with service loader SPI

Changes: https://git.openjdk.org/jdk/pull/19443/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19443&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333131
  Stats: 14 lines in 1 file changed: 14 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19443.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19443/head:pull/19443

PR: https://git.openjdk.org/jdk/pull/19443