Revert "syntax: Remove empty rules in regions"

This reverts commit a9b513a28a.

runtime/syntax/lua.yaml

@@ -45,6 +45,7 @@ rules:
     - constant.string:
         start: "\\[\\["
         end: "\\]\\]"
+        rules: []
 
 # support first few lengths of "long brackets" explicitly
 # brackets longer than that will give false positives
@@ -52,18 +53,22 @@ rules:
     - constant.string:
         start: "\\[=\\["
         end: "\\]=\\]"
+        rules: []
 
     - constant.string:
         start: "\\[==\\["
         end: "\\]==\\]"
+        rules: []
 
     - constant.string:
         start: "\\[===\\["
         end: "\\]===\\]"
+        rules: []
 
     - constant.string:
         start: "\\[====+\\["
         end: "\\]====+\\]"
+        rules: []
 
     - comment.block:
         start: "\\-\\-\\[\\["