Fix kernel configuration for xeus-cpp-lite

[anutosh491]

This is the kernel.json file I see while building xeus-cpp-lite

{
  "display_name": "C++20",
  "env": {
      "PATH":"/Users/anutosh491/micromamba/envs/xeus-cpp/bin:/Users/anutosh491/.pixi/bin:/Users/anutosh491/miniconda3/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/Users/anutosh491/micromamba/condabin:/Users/anutosh491/.pixi/bin:/Users/anutosh491/miniconda3/bin",
      "LD_LIBRARY_PATH":""
  },
  "argv": [
      "/Users/anutosh491/micromamba/envs/xeus-cpp/bin/xcpp",
      "-f",
      "{connection_file}",
      "-resource-dir", "/Users/anutosh491/micromamba/envs/xeus-cpp/lib/clang/19",
      "-I", "/Users/anutosh491/micromamba/envs/xeus-cpp/include",
      "-std=c++20"
  ],
  "language": "cpp",
  "metadata": {"debugger": false
  }
}

Most things are redundant (or can't be used in a wasm context) except

1. kernel display name
2. c++ version based on kernel name
3. language (cpp or c I guess)
4. debugger info

Things like env, resource dir and other include paths if any can't be put to use.
There is no xcpp exectuable either (a wasm build would give us xcpp.js, xcpp.wasm, xcpp.data) and we just have an empty placeholder there.

[anutosh491]

Related #183

[anutosh491]

We should be able to fetch the c++ version out of kernel.json and pass it here

xeus-cpp/src/main_emscripten_kernel.cpp

Lines 18 to 23 in 859a1b9

	EMSCRIPTEN_BINDINGS(my_module)
	{
	xeus::export_core();
	using interpreter_type = xcpp::wasm_interpreter;
	xeus::export_kernel<interpreter_type>("xkernel");
	}

[anutosh491]

https://discord.com/channels/1235591463472074924/1239452863587942440/1308669884539863101

[DerThorsten]

@anutosh491 we still use the name of the "executable" on the javascript side
https://github.com/jupyterlite/xeus/blob/main/jupyterlite_xeus/add_on.py#L48

To get the name of the wasm "binary" we use the first value of the args

[anutosh491]

Probably for the wasm case our kernel.json should look like the following for starters

{
  "display_name": "C++20",
  "argv": [
      "/Users/anutosh491/micromamba/envs/xeus-cpp/bin/xcpp",  (this can be just xcpp or xcpp.wasm if we would like)
      "-std=c++20"
  ],
  "language": "cpp",
  "metadata": {"debugger": false
  }
}