[Feature request] Entry point generation

Please provide an option to manually produce entry points in the DllImport

This already works if we use the -p option but it would be nice if we could do this without -p for post processing steps after ClangSharp

Start by tracing the existing entry-point generation path enabled by the -p option and inspect how DllImport output is handled after ClangSharp runs. Define the new option's expected behavior for post-processing without -p, then verify that entry points are generated in both modes.

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