RFR: JDK-8297299 SequenceInputStream should not use Vector [v2]

[Markus KARG]

> There is no need to use a temporary Vector within the constructor of SynchronizedInputStream, as more efficient (non-synchronized) alternative code (like List.of) will do the same in possibly less time. While the optimization is not dramatic, it still makes sense to replace Vector unless synchronization is really needed.

Markus KARG has updated the pull request incrementally with one additional commit since the last revision:

  allowing s2 to be null

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11249/files
  - new: https://git.openjdk.org/jdk/pull/11249/files/3495a8b2..b6ccec20

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11249&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11249&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11249.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11249/head:pull/11249

PR: https://git.openjdk.org/jdk/pull/11249