RFR: 8372661: Add a null-safe static factory method to "jdk.test.lib.net.SimpleSSLContext" [v2]

[Volkan Yazici]

> Overhauls `SimpleSSLContext` to remove the need for null checks at the call site, and to accept a key store file search path, which removes the need to copy-paste `SimpleSSLContext` just to change the search path.
> 
> ### Tips for reviewers
> 
> 1. Start from `SimpleSSLContext.java`
> 2. See how `test/jdk/java/net/httpclient/whitebox/java.net.http/jdk/internal/net/http/SimpleSSLContext.java` is renamed to `test/jdk/java/net/httpclient/whitebox/java.net.http/jdk/internal/net/http/SimpleSSLContextWhiteboxAdapter.java` and how `@compile/module=java.net.http .../SimpleSSLContext.java` JTreg tag is used to inject `SimpleSSLContext`

Volkan Yazici has updated the pull request incrementally with one additional commit since the last revision:

  Reverted all changes and only kept `SimpleSSLContext` enhancements

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28765/files
  - new: https://git.openjdk.org/jdk/pull/28765/files/326fd60e..d4c9b312

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28765&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28765&range=00-01

  Stats: 1093 lines in 205 files changed: 734 ins; 54 del; 305 mod
  Patch: https://git.openjdk.org/jdk/pull/28765.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28765/head:pull/28765

PR: https://git.openjdk.org/jdk/pull/28765