Now we look for the standard Web Cryptography API before attempting to
check for Node.js support. This allows Node.js ES6 module users to add
a polyfill like:
```js
import {webcrypto} from 'crypto'
globalThis.crypto = webcrypto
```
as described in #256 (comment)

Signed-off-by: Joe Richey <joerichey@google.com>

This allows users to get an actionable error message about this
particular problem. We also add detection for this problem.

Signed-off-by: Joe Richey <joerichey@google.com>

Signed-off-by: Joe Richey <joerichey@google.com>

This call throws an exception if module isn't defined.

Signed-off-by: Joe Richey <joerichey@google.com>

Signed-off-by: Joe Richey <joerichey@google.com>