Remove escape_regex and use Regex.append_source directly for all

#5842 (comment)

It is super tricky way.
But @straight-shoota said, so it is right way also.

src/compiler/crystal/syntax/to_s.cr

@@ -970,7 +970,7 @@ module Crystal
       when StringLiteral
         Regex.append_source exp.value, @str
       when StringInterpolation
-        visit_interpolation(exp) { |s| escape_regex s }
+        visit_interpolation(exp) { |s| Regex.append_source s, @str }
       end
       @str << "/"
       @str << "i" if node.options.includes? Regex::Options::IGNORE_CASE
@@ -979,10 +979,6 @@ module Crystal
       false
     end
 
-    def escape_regex(s)
-      String.build { |io| Regex.append_source s, io }
-    end
-
     def visit(node : TupleLiteral)
       @str << "{"
 

src/regex.cr

@@ -519,7 +519,7 @@ class Regex
   end
 
   # :nodoc:
-  def self.append_source(source, io)
+  def self.append_source(source, io) : Nil
     reader = Char::Reader.new(source)
     while reader.has_next?
       case char = reader.current_char