Create a bespoke runtime manager for VSC

[josephjclark]

This is for much later on when the exension is more mature

Right now the extension just calls out to the CLI to do stuff like execution

This is fine, but the CLI makes a bunch of assumptions and the input and output maybe don't integrate with VSC that nicely

We could build our own runtime manager layer inside VSC - basically a Javascript component which compiles and executes code. It would look a lot like the CLI in that it's a bunch of high level services which collate and organise lower level modules. It could probably re-use a lot of code.