create_test_jar.sh, loading-test{,2}-jar.sh: Migrate dx -> d8

These .sh scripts created .dex files using the dx command.
Since dx is no longer used for Android builds, this CL updates
those scripts to use d8 instead.

This CL also updates the files generated by those scripts.

Since the loading-test* stuff was added in 2011 and barely
touched since then, I had a quick look to see if the jars are
still used. I've found that {,Base}DexClassLoaderTest.java
refers to them.

Test: Ran "unzip -l" on each affected .jar to ensure that the set
      of file paths in them is the same before/after this CL.
      The only difference in set of jar entries was that all of
      the new but not all of the old files had an entry for
      the folder META-INF/ itself rather than only for the file
      META-INF/MANIFEST.MF. I'm guessing that the old files were
      created with an old version of the jar tool.

      I did not examine the *contents* of the files inside the .jars
      or of the .dex files.
Test: atest CtsLibcoreTestCases:libcore.dalvik.system.DexClassLoaderTest

Bug: 119865052

Change-Id: I94314c47d05752e6328a7b1774298a09118e7270