Add demo for JEP 347 - Enable C++14 Language Features (Java 16)

[Abhineshhh]

Description

Implements informational demo for JEP 347 - Enable C++14 Language Features (Java 16).

As discussed with the maintainer, this JEP is an internal JVM/JDK development change with no user-facing Java APIs, so the demo explains what the JEP does and its impact.

Fixes #251

Changes Made

• Added Cpp14FeaturesDemo.java with detailed explanation of:
  • What JEP 347 changes (C++98/03 → C++14 for JDK C++ codebase)
  • Why it matters (better code quality, type safety, performance)
  • Key C++14 features now available (generic lambdas, auto, constexpr, etc.)
  • Impact on Java developers (transparent, indirect benefits)
• Added JEP 347 entry to JDK16Info.json (ordered between 338 and 380)
• Registered demo in Java16.java initializer

Checklist

• Follows contribution guide
• Proper Markdown-style documentation with JEP history and further reading
• Calls info(347) as first statement
• JSON entry added in correct numerical order
• Demo registered in Java16.java with // JEP 347 comment
• No unrelated changes
• Informational demo (no code examples, as agreed with maintainer)

[AloisSeckar]

Hi @Abhineshhh and thank you for your contribution. There are two minor changes that should be made before this PR gets merged. Please, have a look.

[Abhineshhh]

done @AloisSeckar