Ship packages as bundled and untranspiled code

The npm packages in the toolkit all ship with non-bundled and heavily transpiled code, for example https://unpkg.com/@actions/cache@1.0.6/lib/cache.js starts like this:

var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
    function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
    return new (P || (P = Promise))(function (resolve, reject) {
        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
        function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
        function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
        step((generator = generator.apply(thisArg, _arguments || [])).next());
    });
};

Using vcc as is recommended by for example the typescript starter example, I end up with a bundle like this (from https://github.com/Swatinem/rust-cache):

> grep "var __awaiter =" dist/save/index.js | wc -l
13

Actions are running on at least node 12 by definition, and they can run async/await code untranspiled. I wonder how much smaller, and faster to execute the final action would be if we could trim out all this unnecessary and duplicated code.

As a contributor to rollup and maintainer of https://github.com/Swatinem/rollup-plugin-dts I could very well whip up something to improve the situation, but I don’t really want my efforts to be in vain, seeing that most of the PRs to this repo go stale and unmerged :-(

Start by inspecting how the toolkit's npm packages are built and the generated dist/save/index.js mentioned in the issue, along with the TypeScript starter example using vcc. Compare bundled output for duplicated __awaiter helpers and untranspiled async/await. Done means the packages produce smaller, bundled output without unnecessary transpilation, with any relevant size or execution improvements measured.