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/tools/lsp/autoload.el

@@ -0,0 +1,7 @@
+;;; feature/lsp/autoload.el -*- lexical-binding: t; -*-
+
+;;;###autoload
+(defun +lsp|init ()
+  "Enable LSP as late as possible, to allow users to customize it via file or
+dir local variables."
+  (add-hook 'hack-local-variables-hook #'lsp nil t))

modules/tools/lsp/config.el

@@ -0,0 +1,21 @@
+;;; tools/lsp/config.el -*- lexical-binding: t; -*-
+
+(def-package! lsp-ui
+  :hook (lsp-mode . lsp-ui-mode)
+  :config
+  (setq lsp-prefer-flymake nil
+        lsp-ui-doc-max-height 8
+        lsp-ui-doc-max-width 35
+        lsp-ui-sideline-ignore-duplicate t)
+  (define-key! lsp-ui-mode-map
+    [remap xref-find-definitions] #'lsp-ui-peek-find-definitions
+    [remap xref-find-references]  #'lsp-ui-peek-find-references)
+  (set-lookup-handlers! 'lsp-ui-mode
+    :definition #'lsp-ui-peek-find-definitions
+    :references #'lsp-ui-peek-find-references))
+
+(def-package! company-lsp
+  :when (featurep! :completion company)
+  :after lsp-mode
+  :config
+  (set-company-backend! 'lsp-mode 'company-lsp))

modules/tools/lsp/packages.el

@@ -0,0 +1,7 @@
+;; -*- no-byte-compile: t; -*-
+;;; tools/lsp/packages.el
+
+(package! lsp-mode)
+(package! lsp-ui)
+(when (featurep! :completion company)
+  (package! company-lsp))