Back ported the timer util that returns a scaled down timer value in test environments

[tgvrssanthosh]

Summary

Created timer util that returns a scaled-down timer value in the test environments.

Details

ember-lifeline methods such as runTask, debounceTask defer execution of the callback function passed to them by the amount of timer value that is passed to these functions. Under the hood, It uses ember runloop's methods which in turn will be delegated to backburner.

Since these tasks are delegated to the backburner, they fall under ember-aware async constructs. Due to this, the async ember test util settled (click, render etc., internally uses the settled method) will wait for all the pending async timer functions to be completed and then the test execution flow will proceed to the next line.

Let's say we are debouncing the task of making a request to API to fetch the typeahead results by 300ms. It means that the test will wait for at least 300ms to make an API call (which can be mocked using pretender or ember-cli-mirage). Ideally, in test environments, there is no need to wait as the necessary input will be added programmatically as opposed to the user typing manually (in which case it makes sense to defer by 300ms owing to the typing speed of a user)

Hence, I have added a util method to return a scaled-down version of the timer in the test environments. By default, it will scale down the timer value by 100x. If a second argument is passed, the second value will be returned in the test environment.

[scalvert]

We can't make this change in the v6 branch. Changing node engines is a breaking change, and as such it's not possible to do.

[scalvert]

I'm not sure we should be bumping addon-docs all the way up to this version. I'd prefer we do minimal changes in this release branch, and defer changes to the master branch.

[elwayman02]

@tgvrssanthosh can you update this PR according to the review feedback, to avoid introducing breaking changes?

[elwayman02]

Please rebase now that #1149 is merged.