replace tsc with swc for compiling TS source

[mayank99]

Changes

Previously, only tsc (TypeScript compiler) was being used to compile the .tsx/.ts source into .js and .d.ts files. This works, but is not very flexible and is super slow.

This PR changes the build process so that swc is used for generating the actual code (.js), and tsc is only used for generating types (.d.ts). This is faster, but more importantly, it allows much greater control over the build output.

In this PR, I've used swc to strip all code comments (something that tsc cannot do). In future PRs, I plan to make other changes to the output.

While verifying the build output, I also noticed that the prettier script (added in #1389) wasn't working, so I fixed it by changing the ignore-path.

Testing

Manually verified that the build output looks fine. CI is also passing, which means that dependent workspaces (react-workshop/e2e/a11y tests and all playgrounds) are happy with the output.

Further testing pending (at minimum I would like to test in webpack/CRA).

Docs

Added changesets, since this is a user-facing change.

[Ben-Pusey-Bentley]

Looks good. Tested this out with a rudimentary create react app project, and it seems to work. screenshot:

App.js file:

import { Button, ThemeProvider } from '@itwin/itwinui-react';
import './App.css';

function App() {
  return (
    <ThemeProvider>
      <Button>Hello world</Button>
    </ThemeProvider>
  );
}

export default App;