Backport p7zip_jll infrastructure changes from f03e9c3
Bring over the p7zip_jll handling improvements from f03e9c3 ([deps] enable zstd support):
- Move p7zip binary from bindir to private_libexecdir
- Add Windows DLL handling for binary builder installs
- Simplify p7zip_jll.jl by removing LIBPATH handling
- Add P7ZIP_BUILD_OPTS variable for consistent build flags
These changes prepare for the p7zip 17.7.0 upgrade and ensure p7zip
is installed in the correct location.
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Co-Authored-By: Claude <noreply@anthropic.com>