RFR: 8287442: Reduce list to array conversions in java.lang.invoke.MethodHandles

[Claes Redestad]

In preparation of #8855 this PR refactors the conversions from `List` to array and array to `List`, reducing the number of conversions when calling `MethodHandles.dropArguments` in particular. This remove about ~5% of allocations on the `StringConcatFactoryBootstraps` microbenchmark.

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Commit messages:
 - Move all conversions closer to the edge
 - Merge master
 - Streamline MHs.dropArguments parameter handling
 - Missed correctly taking b1 into account in of(byte, int, int...) (java/lang/String/concat/ImplicitStringConcatShapes.java test failure)
 - Address review comments, fix unsafe shift, rework and remove ofBothArrays
 - Revert unrelated and unverified hashCode change
 - Improve TransformKey to pack more kinds of transforms efficiently

Changes: https://git.openjdk.java.net/jdk/pull/8923/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8923&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287442
  Stats: 46 lines in 3 files changed: 9 ins; 3 del; 34 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8923.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8923/head:pull/8923

PR: https://git.openjdk.java.net/jdk/pull/8923