Consider having a size budget for axe-core

[straker]

From the discussion on GoogleChrome/lighthouse#10056, axe 3.4.0 added 60KB minified to our codebase, mostly from the addition of core-js Unit32Array polyfills 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)

[scurker]

@straker I've put some of this in place already with the extension, so hit me up if you want to pair on this for axe-core.

[WilcoFiers]

Dropped axe-core's filesize from 138kb in 4.0 to 108kb in 4.1! For 4.2 we should put tests in place to enforce a maximum size.

[dylanb]

Can we add a performance budget too? Some of the techniques for reducing size, may increase execution time.

[straker]

I like the idea of a performance budget. We'll probably want to separate our metrics into different size pages or buckets though as some rules perform worse on very large pages but this may be acceptable for the rule itself.