feature/lookup: rewrite dash docset integration

+ Uses alist variable to store config, rather than hooks
+ Added check for installed docsets in +lookup/documentation
+ Set docsets for various language modules (c-mode, c++-mode, css-mode,
  scss-mode, sass-mode, web-mode, go-mode, racket-mode, emacs-lisp-mode,
  js2-mode, rjsx-mode, typescript-mode, rust-mode, and php-mode)
+ Made *eww* popups for dash docsets larger
+ Renamed set-docset! => set-docsets! (set-docset! is aliased to
  set-docsets!)
+ New +lookup/install-docset alias

modules/lang/rust/config.el

@@ -2,7 +2,7 @@
 
 (after! rust-mode
   (set-env! "RUST_SRC_PATH")
-  (set-docset! 'rust-mode "Rust")
+  (set-docsets! 'rust-mode "Rust")
   (setq rust-indent-method-chain t)
 
   (map! :map rust-mode-map