RFR: 8320971: Use BufferedInputStream.buf directly when param of implTransferTo() is trusted [v8]

[Sergey Tsypanov]

> It looks like we can skip copying of `byte[]` in `BufferedInputStream.implTransferTo()` for `OutputStreams` residing in `java.io`.
> 
> See comment by @vlsi in https://github.com/openjdk/jdk/pull/10525/files#diff-e19c508d1bb6ee78697ecca66947c395adda0d9c49a85bf696e677ecbd977af1R612

Sergey Tsypanov has updated the pull request incrementally with one additional commit since the last revision:

  8320971: Extract utility class

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16879/files
  - new: https://git.openjdk.org/jdk/pull/16879/files/6abc46d4..f5cf1346

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16879&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16879&range=06-07

  Stats: 73 lines in 4 files changed: 53 ins; 17 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/16879.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16879/head:pull/16879

PR: https://git.openjdk.org/jdk/pull/16879