highlighter: Fix regions and patterns inside regions (#2840)

* highlighter: Fix regions and patterns inside regions

* highlighting: Remove 2nd recursive highlightRegion() call

...and add limitGroup checks to pattern search.

* yaml: Add TODO type highlighting

* highlighting: Don't stop in highlightRegion() at empty lines

...because possible region line end pattern must be detected.

* syntax/sh: Correct string handling due to additional pattern handling

* syntax/sh: Remove slash in variables

* highlighter: Accept nested region only in case it's within the current reagion

* highlighter: Accept nested patterns only in case it's within the current reagion

* highlighter: Don't search for nesting in case the region end was found at start

runtime/syntax/sh.yaml

@@ -42,18 +42,18 @@ rules:
     - statement: " (-[A-Za-z]+|--[a-z]+)"
 
     - identifier: "\\$\\{[0-9A-Za-z_:!%&=+#~@*^$?, .\\-\\/\\[\\]]+\\}"
-    - identifier: "\\$[0-9A-Za-z_:!%&=+#~@*^$?,\\-\\/\\[\\]]+"
+    - identifier: "\\$[0-9A-Za-z_:!%&=+#~@*^$?,\\-\\[\\]]+"
 
     - constant.string:
         start: "\""
         end: "\""
         skip: "\\\\."
-        rules:
-            - constant.specialChar: "\\\\."
+        rules: []
 
     - constant.string:
         start: "'"
         end: "'"
+        skip: "\\\\."
         rules: []
 
     - comment: