Feature request: `injectScriptOnce`

[bantic]

A pattern we commonly use is to use a utility function to inject a script (for example, the filestack SDK) and keep a reference to the promise, returning it for subsequent calls so that multiple script elements don't get added to the page.

Would you be interested in a PR that adds an injectScriptOnce function that uses a map to keep track of which URLs have already been injected, and return their existing promise instead of creating a new <script> tag?

[rlivsey]

Sounds good to me 👍