[WIP] Cargo binding lib

[afinch7]

First pass at a cargo binding based on the WIP native binding api in denoland/deno#2385
This is intended as a bootstrapping tool for other native bindings.
Example usage:

import { build } from "https://deno.land/std/cargo/mod.ts";
import { join, dirname } from "https://deno.land/std/fs/path/mod.ts";

const { dlopen, dlname } = Deno;

const manifest_path = join(dirname(import.meta.url), "Cargo.toml");
const buildResult = build({
    manifest_path,
});
// We could also search through the artifacts list here to find something more specific if we wanted. 
const dlib = dlopen(join(buildResult.output_root, dlname(buildResult.artifacts[0].output_name)));
const someOp = dlib.loadFn("some_op");

This should work on any machine that has at least a version of rustc installed.

[CLAassistant]

All committers have signed the CLA.

[ry]

Nice!

[afinch7]

This is working with tests and all instructions if you want to test:

1. Build deno cli from my native bindings branch. Last tested with this commit afinch7/deno@34bc878 you will need to update sub modules recursively (still waiting on the new version of dlopen-derive to get published).
2. You need to make sure that the dependency config for deno in the Cargo.toml files points to //core in the clone of my branch used to build deno.
3. cargo build --release -p deno_cargo_plugin
4. DL_PATH_CARGO_BINDING=$PWD/target/release/libdeno_cargo_plugin.so <PATH_TO_DENO_BINARY> run --allow-all --config=tsconfig.test.json cargo/run_test.ts

If everything is setup correctly it should automatically build the test binding and then run tests on it.