Updates `HttpClientImpl.DelegatingExecutor` to resort to the fallback executor only on `RejectedExecutionException`. `DelegatingExecutorTest` is added to verify the behavior of `DelegatingExecutor`. `tier1,2` reports are attached to the ticket.
------------- Commit messages: - Handle only `RejectedExecutionException` in `HttpClientImpl.DelegatingExecutor` Changes: https://git.openjdk.org/jdk/pull/23713/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23713&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8350019 Stats: 209 lines in 3 files changed: 206 ins; 0 del; 3 mod Patch: https://git.openjdk.org/jdk/pull/23713.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/23713/head:pull/23713 PR: https://git.openjdk.org/jdk/pull/23713
