[code-reflection] Integrated: move ffi cpp and include files under ./src/main/native

[Gary Frost]

On Fri, 20 Jun 2025 15:45:13 GMT, Gary Frost <gfrost at openjdk.org> wrote:

> Previously *.cpp and *.include files were in the backend root dir (under cpp/*.cpp and include/*.h)
> 
> Now these files are pushed down to mimic maven src layout
> 
> /src/main/
>       java/
>           hat/backend packages
>       native/cpp/
>            *.cpp
>       native/include
>           *.h  
> ```      
> 
> Also we build a separate shared_backend.so rather than pulling the  source from shared dir into each backend.

This pull request has now been integrated.

Changeset: a8348857
Author:    Gary Frost <gfrost at openjdk.org>
URL:       https://git.openjdk.org/babylon/commit/a83488579e49f2f39c61ea1e31e126df9e3e8e46
Stats:     136 lines in 50 files changed: 46 ins; 48 del; 42 mod

move ffi cpp and include files under ./src/main/native

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PR: https://git.openjdk.org/babylon/pull/453