Add highlighting query for Scss @for loops

The Scss language only had highlighting queries for `@each` loops, this
commit adds support for `@for` loops as well.

Also moved all loop-related keywords (including newly added ones) to
`@repeat` rather than `@keyword`

queries/scss/highlights.scm

@@ -3,11 +3,18 @@
 [
   "@mixin"
   "@media"
-  "@while"
-  "@each"
   "@include"
 ] @keyword
 
+[
+  "@while"
+  "@each"
+  "@for"
+  "from"
+  "through"
+  "in"
+] @repeat
+
 (single_line_comment) @comment
 (function_name) @function
 
@@ -29,6 +36,9 @@
 (each_statement (value) @parameter)
 (each_statement (variable_value) @parameter)
 
+(for_statement (variable) @parameter)
+(for_statement (_ (variable_value) @parameter))
+
 (argument) @parameter
 (arguments (variable_value) @parameter)