RFR: 8336470: Source launcher should work with service loader SPI in unnamed module [v12]

[Christian Stein]

> Please review this change adding a missing resource file test to the `MemoryClassLoader::findResource` override in order to resolve all files beneath the source root path in source launch mode - analog to what was already implemented for `MemoryClassLoader::getResource`.
> 
> With this change applied, files in `META-INF/services/` are resolved; allowing services providers being supplied in source form.

Christian Stein has updated the pull request incrementally with one additional commit since the last revision:

  Prevent NPE by removing redundant check

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20193/files
  - new: https://git.openjdk.org/jdk/pull/20193/files/c921f2c9..79dde479

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20193&range=11
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20193&range=10-11

  Stats: 5 lines in 1 file changed: 0 ins; 3 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/20193.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20193/head:pull/20193

PR: https://git.openjdk.org/jdk/pull/20193