RFR: 8320971: Use BufferedInputStream.buf directly when param of implTransferTo() is trusted [v16]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 20 additional commits since the last revision:

 - 8322292: Remove TransferToTrusted.checkedOutputStream()
 - 8320971: Adjust JavaDoc
 - Merge branch 'master' into 8320971
 - 8320971: Revert irrelevant changes
 - 8320971: Add more tests
 - 8320971: Fix JavaDoc
 - 8320971: Whitespaces
 - 8320971: Fix build
 - 8320971: Move IOStreams to com.sun.io
 - Merge branch 'master' into 8320971
 - ... and 10 more: https://git.openjdk.org/jdk/compare/b8f084e1...84686bc6

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/16879/files
  - new: https://git.openjdk.org/jdk/pull/16879/files/8626e926..84686bc6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16879&range=15
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16879&range=14-15

  Stats: 3675 lines in 269 files changed: 2030 ins; 696 del; 949 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