Migrates `test/jdk/com/sun/net/httpserver/` to null-safe `SimpleSSLContext` methods introduced in [JDK-8372661], which is a prerequisite for this change set.
------------- Commit messages: - Restore `test/jdk/com/sun/net/httpserver/` changes - Make sure `get()` returns the same instance - Reverted all changes and only kept `SimpleSSLContext` enhancements - Overhaul `SimpleSSLContext` and its usages Changes: https://git.openjdk.org/jdk/pull/28800/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28800&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8373537 Stats: 136 lines in 16 files changed: 52 ins; 24 del; 60 mod Patch: https://git.openjdk.org/jdk/pull/28800.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/28800/head:pull/28800 PR: https://git.openjdk.org/jdk/pull/28800
