Upgrade to jupyterlite-xeus 3

[anutosh491]

The deploy build for xeus-cpp-lite (on both xeus-cpp & cppinterop) were failing yesterday as there as pointed out by @mcbarton on discord. This is because there was a release on jupyterlite-xeus yesterday.

The improvements that have been worked on

1. Jupyterlite-xeus 3 depends on mambajs that basically helps Installing conda packages into a browser. So basically we need this if we plan on supporting numcpp, xtensor, clad or anything in the browser.

2. There won't be a need to copy stuff as we are doing currently

cp $PREFIX/bin/xcpp.data _output/extensions/@jupyterlite/xeus/static
cp $PREFIX/lib/libclangCppInterOp.so _output/extensions/@jupyterlite/xeus/static

Prs were made to handle the .data and the .so file

For reference
i) This PR by me handles the .data file
jupyterlite/xeus#145
ii) This PR by Martin Renou (a maintainer) handles the .so file
jupyterlite/xeus#146

So a simple jupyterlite build and jupyterlite serve would be enough here.

[anutosh491]

How do we go about the upgrade.

1. We need a way to include missing Emscripten APIs. Otherwise we would encounter issues like this (TypeError while running xeus-cpp with jupyterlite-xeus 3.0.0a2 jupyterlite/xeus#141)

Currently the best way to fix this is through a post.js file like done in xeus-r (jupyter-xeus/xeus-r#113) untill we have a way to shift this change in xeus-lite so that all kernels automatically including this change.

2. After the update, as the shared object file would now be automatically picked up, we need to let jupyterlite-xeus know what shared object file would xeus-cpp-lite depend on. Hence we need to update our kernel.json something like this (Specify needed shared libs in kernel spec jupyter-xeus/xeus-r#114)

So we would need something like the following in our kernel.json !

    "shared": {
      "libclangCppInterOp.so": "lib/libclangCppInterOp.so"
    }
    

This also gives me a reason to maybe split out the kernel.json to build a separate thing for the wasm build and for the non-wasm build as I've pointed out here (#185)

[anutosh491]

First PR for solving this is up (#220)

[anutosh491]

Second Pr that should fix this issue is now raised #221