Allow \S for negated whitespace regex shorthand

spec/compiler/prepare_grammar/parse_regex_spec.cc

@@ -30,7 +30,7 @@ describe("parse_regex", []() {
 
     {
       "character classes",
-      "\\w-\\d-\\s",
+      "\\w-\\d-\\s-\\S",
       seq({
         character({
           'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
@@ -41,7 +41,10 @@ describe("parse_regex", []() {
         character({ '-' }),
         character({ '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' }),
         character({ '-' }),
-        character({ ' ', '\t', '\r', '\n' }) })
+        character({ ' ', '\t', '\r', '\n' }),
+        character({ '-' }),
+        character({ ' ', '\t', '\r', '\n' }, false)
+      })
     },
 
     {

src/compiler/prepare_grammar/parse_regex.cc

@@ -192,6 +192,13 @@ class PatternParser {
       case 's':
         return CharacterSet().include(' ').include('\t').include('\n').include(
           '\r');
+      case 'S':
+        return CharacterSet()
+          .include_all()
+          .exclude(' ')
+          .exclude('\t')
+          .exclude('\n')
+          .exclude('\r');
       case 't':
         return CharacterSet().include('\t');
       case 'n':