[sil-mode.el] Improve handling of box types by sil-mode-display-function-cfg

Specifically, I changed how sil-mode-display-function-cfg searches for the
start/end of the SIL function body where the current point is. Previously, we
just searched for the exact strings "{" and "}" backwards and forwards
respectively. That was insufficient in the context of box types that use those
characters.

Instead with this change, we convert the aforementioned static search to a regex
search. Our regex match "{$" for the beginning of the SIL function and "^} //
end sil function '" or "^}" which I think will generally work to get the correct
body. NOTE: We first check for the end sil function variant.

Author: gottesmm

utils/sil-mode.el

@@ -275,16 +275,20 @@
 
 (defun sil-mode-display-function-cfg()
   (interactive)
-  ;; First we need to find the previous '{' and then the next '}'
+  ;; First we need to find the previous '{' and then the next '}'.
   (save-mark-and-excursion
-   (let ((brace-start (search-backward "{"))
-         (brace-end (search-forward "}"))
-         (process-connection-type nil))
-     (let ((p (start-process sil-mode-viewcfg-program-name
-                             sil-mode-viewcfg-buffer-name
-                             sil-mode-viewcfg-command
-                             (concat "--renderer=" sil-mode-viewcfg-renderer))))
-       (process-send-region p brace-start brace-end)
+    (let ((brace-start (re-search-backward "{\s*$"))
+          (brace-end (re-search-forward "^} // end sil function '" nil t))
+          (process-connection-type nil))
+      ;; See if we failed to find } // end sil function. If we did, search again
+      ;; for ^} itself and see if we find anything.
+      (if (null brace-end)
+          (setq brace-end (re-search-forward "^}")))
+      (let ((p (start-process sil-mode-viewcfg-program-name
+                              sil-mode-viewcfg-buffer-name
+                              sil-mode-viewcfg-command
+                              (concat "--renderer=" sil-mode-viewcfg-renderer))))
+        (process-send-region p brace-start brace-end)
        (process-send-eof p)))))
 
 ;;; Top Level Entry point