Consider having a size budget for axe-core

From the discussion on https://github.com/GoogleChrome/lighthouse/pull/10056, axe 3.4.0 added 60KB minified to our codebase, mostly from the addition of [core-js Unit32Array polyfills](https://github.com/GoogleChrome/lighthouse/pull/10056#issuecomment-562360821) needed for the ligature icon detection. This pushed lighthouse over their size budget, causing them to fail their build.

For 4.0.0 we should consider introducing a size budget ourselves so we don't continue to increase in size (as we have done as shown by @patrickhulce chart)