Webcil Loader Support for Corerun

[adamperlin]

We now have browser host webcil loader support as our starting point for a Webcil loader for CoreCLR. For Wasm R2R testing purposes and quick dev iteration, it would be nice to have corerun support as well, so that ideally we could test webcil assembly loading/execution in JavaScript in the cli with a single command like:

node corerun.js -c <IL_ROOT> <my-webcil-assembly>.wasm

cc @pavelsavara

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