Keep it on platforms requiring a non-const buffer. These are AmigaOS and
OS400.
Also:
- replace `SEND_QUAL_ARG2` with boolean macro `SEND_NONCONST_ARG2`.
Closes#20463
To simplify the directory layout.
- OS400 and vms support move from `packages` to `projects`.
- Windows README and `generate.bat` files move from `projects`
to `projects/Windows`.
Closes#20271