[lworld] RFR: 8281763: Support Valhalla class file features in asmtools

[Dan Smith]

Modifying the Valhalla repo's fork of asmtools to implement Valhalla class file features:

- ACC_VALUE, ACC_PERMITS_VALUE, and ACC_PRIMITIVE 
- Preload attribute 
- aconst_init & withfield instructions 
- Unnamed factory methods 
- Q descriptors

Mainly relevant to the `jasm` tool, but there are also some interactions with `jdis` and `jdec`. No impact on `jcod`.

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Commit messages:
 - Merge branch 'asmtools' into asmtools-valhalla
 - Merge branch 'lworld' into asmtools
 - Modified asmtools files
 - AsmTools updates for Valhalla features
 - Merge branch 'lworld' into asmtools
 - Fix trailing whitespace
 - Added usage comment
 - Generalize JtregDriver for all asmtools commands
 - Add JtregDriver to provide an entry point that doesn't call System.exit
 - Add asmtools source to test/lib

Changes: https://git.openjdk.java.net/valhalla/pull/647/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=647&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281763
  Stats: 189 lines in 14 files changed: 165 ins; 6 del; 18 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/647.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/647/head:pull/647

PR: https://git.openjdk.java.net/valhalla/pull/647