Add throttling to download progress events

[KleggerKoder]

Platforms affected

iOS and Android

Motivation and Context

Way too many progress events being fired and makes all the application side progress indicators bounce around and sometimes crash the app. I believe download speeds may have affected the number of updates as well.

Description

Added some throttling to reduce message rate to 1/100th what it use to.

Testing

1/100th seemed reasonable for downloading a variety of small and large files on fast connections.
Your experience may vary depending on connection speeds.

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[wilk-polarny]

Hi, I would like to suggest a different approach, since fixing the underlying Cordova issue is arduous.
Rather than always skipping 100 elements, I would suggest to:

a) Only emit computable events
b) compute and track the progress and only emit an event if the current progress changed significantly. For example, computer the progress %, and only emit an event every 1% - or once a certain amount of transferred bytes has been reached - based on the content length.