[lldb-dap] VSCode extension doesn't report partly-incompatible/supported versions

I encountered https://github.com/llvm/llvm-project/issues/123055 (env not working) because the documentation on the lldb-dap info page led me to believe that LLVM 19 was required for compatibility:

The missing `env` support took some time to debug and there was no warning about incompatibility. I suggest as a fix:
1. Update the documentation to say `LLVM-{version}-{operating_system}.tar.xz` and possibly report the range of supported/recommened versions?
2. Exit with a fatal error if user-requested features like `env` are unsupported with the given version of lldb-dap

Thanks for the great tool!

Start with the lldb-dap info page and the VSCode extension’s handling of the user-requested `env` feature and LLVM versions. Compare the documented `LLVM-{version}-{operating_system}.tar.xz` guidance with the versions actually supported, then verify that documentation and incompatibility reporting clearly cover the requested behavior.

Written by the indexing model from the issue text.