RFR: 8287442: Reduce list to array conversions in java.lang.invoke.MethodHandles [v2]

[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.

Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:

  Review comments, eagerly convert sooner in tryFinally

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8923/files
  - new: https://git.openjdk.java.net/jdk/pull/8923/files/019e2ef8..15ff2125

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8923&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8923&range=00-01

  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 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