Performance problem with @apply

[axelhzf]

Describe the problem:

After upgrading from tailwind 1.x to 2.x in a project (a nuxt application), our dev server starting times went from ~0.50s to ~1.3s. After some research, we found that the problems are vue components using @apply.

Our profiling looks like this

Most of the time is spent on the buildUtilityMap function. It's taking more than 100ms per component.
After analyzing the function, it looks like it does two things:

• Generate the utilityMap for the lookupTree
• Generate the utilityMap for the css defined by the component

I think we could follow the same approach used on #3032 and memoize the part of the function that won't change over time (the utilityMap for the lookupTree)

I will try to create a PR