Move :tools fly{check,spell} to :checkers {syntax,spell}

These modules were renamed so we can later generalize their
implementations, such as adding flymake support to the syntax checker.

modules/checkers/syntax/autoload.el

@@ -0,0 +1,25 @@
+;;; checkers/syntax/autoload.el -*- lexical-binding: t; -*-
+
+;;;###autodef
+(defun set-next-checker! (mode checker next &optional append)
+  "TODO"
+  (let ((fn (intern (format "+syntax--init-checkers-for-%s-h" mode))))
+    (fset fn
+          (lambda ()
+            (if (not (bound-and-true-p flycheck-mode))
+                (add-hook 'flycheck-mode-hook fn 'append 'local)
+              (flycheck-add-next-checker checker next append)
+              (remove-hook 'flycheck-mode-hook fn 'local))))
+    (add-hook (intern (format "%s-hook" mode)) fn)))
+
+;;;###autoload
+(defun +syntax-init-popups-h ()
+  "Activate `flycheck-posframe-mode' if available and in GUI Emacs.
+Activate `flycheck-popup-tip-mode' otherwise.
+Do nothing if `lsp-ui-mode' is active and `lsp-ui-sideline-enable' is non-nil."
+  (unless (and (bound-and-true-p lsp-ui-mode)
+               lsp-ui-sideline-enable)
+    (if (and (fboundp 'flycheck-posframe-mode)
+             (display-graphic-p))
+        (flycheck-posframe-mode +1)
+      (flycheck-popup-tip-mode +1))))