Added syntax_suggest cli and resolve failing exapmle with it

Merged: https://github.com/ruby/ruby/pull/6287

libexec/syntax_suggest

@@ -0,0 +1,7 @@
+#!/usr/bin/env ruby
+
+require_relative "../lib/syntax_suggest/api"
+
+SyntaxSuggest::Cli.new(
+  argv: ARGV
+).call

spec/syntax_suggest/integration/exe_cli_spec.rb

@@ -5,8 +5,12 @@ require_relative "../spec_helper"
 module SyntaxSuggest
   RSpec.describe "exe" do
     def exe_path
+      if ruby_core?
+        root_dir.join("../libexec").join("syntax_suggest")
+      else
         root_dir.join("exe").join("syntax_suggest")
       end
+    end
 
     def exe(cmd)
       out = run!("#{exe_path} #{cmd}", raise_on_nonzero_exit: false)

spec/syntax_suggest/spec_helper.rb

@@ -43,6 +43,10 @@ def fixtures_dir
   spec_dir.join("fixtures")
 end
 
+def ruby_core?
+  !root_dir.join("syntax_suggest.gemspec").exist?
+end
+
 def code_line_array(source)
   SyntaxSuggest::CleanDocument.new(source: source).call.lines
 end