RFR: 8309259: Reduce calls to MethodHandles.lookup() in jdk.internal.net.http.Stream

[Nizar Benalla]

Please review this simple enhancement that is just reducing the number of times we call the `MethodHandles.lookup()` method, as it can be a bit slow.

TIA

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Commit messages:
 - Update Copyright
 - reduced number of calls to `MethodHandles.lookup()`

Changes: https://git.openjdk.org/jdk/pull/18862/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18862&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309259
  Stats: 4 lines in 1 file changed: 1 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/18862.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18862/head:pull/18862

PR: https://git.openjdk.org/jdk/pull/18862