Add basic LSP support

Still needs to be documented, but includes support for the following
languages:

+ C/C++/ObjC
+ Go
+ Java
+ Javascript
+ OCaml
+ PHP
+ Python
+ Ruby
+ Scala
+ Swift
+ HTML/CSS

Relevant to #460, #716, #1186

modules/lang/php/config.el

@@ -12,9 +12,11 @@
   (set-lookup-handlers! 'php-mode :documentation #'php-search-documentation)
   (set-formatter! 'php-mode #'php-cs-fixer-fix)
 
-  ;; `+php-company-backend' uses `company-phpactor', `php-extras-company' or
-  ;; `company-dabbrev-code', in that order.
-  (set-company-backend! 'php-mode '+php-company-backend 'company-dabbrev-code)
+  (if (featurep! +lsp)
+      (add-hook 'php-mode-hook #'+lsp|init)
+    ;; `+php-company-backend' uses `company-phpactor', `php-extras-company' or
+    ;; `company-dabbrev-code', in that order.
+    (set-company-backend! 'php-mode '+php-company-backend 'company-dabbrev-code))
 
   ;; Use the smallest `sp-max-pair-length' for optimum `smartparens' performance
   (setq-hook! 'php-mode-hook sp-max-pair-length 5)
@@ -32,6 +34,7 @@
 
 
 (def-package! phpactor
+  :unless (featurep! +lsp)
   :after php-mode
   :config
   (set-lookup-handlers! 'php-mode