User experience for showing failed assertions

Following up with https://github.com/GoogleChrome/lighthouse-ci/pull/97 and moving discussion here before creating one more PR 😃

Some of the users are running into an issues when failed assertion results for resource-summary are not transparent when comparing with budget (for example - treosh/lighthouse-ci-action#13, part of the problem is fixed via #97).

E.g. I setup budget for 1KB, but actual value is ~17387 bytes. What will be seen in console is something like this:

expected: <=100
found: 17387

For better UX, I propose something like we have in LH:

expected: <=1.00 KB
found: 16.98 KB

Here is comparison of logs before and after the proposal:

We actually need to define:

• are we ok with KB?
• what fields has to be transformed: resource-summary, others?

[patrickhulce]

In 6.0 we finally have numericUnit so we can address this.

[brendankenny]

@exterkamp I think that’s slightly different because all the units are available for those numbers (we just don’t use them responsibly 😃. I added a note in https://github.com/GoogleChrome/lighthouse/issues/7238#issuecomment-554758706 about solving that using the new Intl.NumberFormat unit formatting that came with Node 12.13 (the new LTS).