Fix @apply selector rewriting when multiple classes are involved

[thecrypticace]

This PR fixes two problems when using @apply:

1. Incorrect placement of element selectors when multiple classes are joined in a selector

Given:

.foo.bar { color: red; }
section { @apply bar; }

We would naively replace the .bar portion with section producing .foosection which is obviously wrong. This did not happen when applying foo because this simple replacement produced something that happened to be correct section.bar.

2. Only replacing the first occurrence of a candidate in a selector: (reverted due to this not being 100% correct either)

Given:

.foo + .foo { color: red; }
section { @apply foo; }

We would produce:

section + .foo { color: red; }

This is not correct because the foo class may not even exist at all if .foo + .foo is defined in the components or utilities layers.

Fixes #9093