Optimize some regex matching (#15528)

* Use Regex#match?

* Replace =~ too

* Avoid to call match? from Nil

* Keep value of Regexp.last_match

app/lib/formatter.rb

@@ -222,7 +222,7 @@ class Formatter
 
     escaped = text.chars.map do |c|
       output = begin
-        if c.ord.to_s(16).length > 2 && UNICODE_ESCAPE_BLACKLIST_RE.match(c).nil?
+        if c.ord.to_s(16).length > 2 && !UNICODE_ESCAPE_BLACKLIST_RE.match?(c)
           CGI.escape(c)
         else
           c