RFR: 8298177: Various java.lang.invoke cleanups

[Claes Redestad]

Various code cleanups around java.lang.invoke code. Started out with dead code removal in `jli.MemberName`, then piled on to fix a set of minor inefficiencies (excessive vararg array allocations, unnecessary defensive cloning of parameter arrays etc).

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Commit messages:
 - Restore but rename test*Flags
 - Various cleanups in java.lang.invoke

Changes: https://git.openjdk.org/jdk/pull/11540/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11540&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298177
  Stats: 259 lines in 9 files changed: 18 ins; 184 del; 57 mod
  Patch: https://git.openjdk.org/jdk/pull/11540.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11540/head:pull/11540

PR: https://git.openjdk.org/jdk/pull/11540