Put Stringbuilder-based code inside clj block

[Joseph-Alley]

The hickory cljc file uses Stringbuilder, even though it is java code. The relevant function is only ever called from clj, but its existence in the cljc file causes some cljs compilation warnings.

This PR puts that code inside a clj block, to prevent warnings.

Note the code would be nicer if we removed the clj-html-escape-without-quoin function entirely, since it exists only to be called within html-escape, which already uses a clj block. However, I didn't want to break the functionality for any users who might be calling clj-html-escape-without-quoin directly, for some reason.

[danielcompton]

Thanks!