Preserve html_safe? status on ActiveSupport::SafeBuffer#*

[r7kamura]

Summary

separator = tag(:br) * 2 #=> "<br /><br />"
separator.html_safe? #=> `nil` on Rails 5.2.3, but it would be nice if this returns `true`.

[kamipo]

This is good to me. Can you add CHANGELOG entry?

[kamipo]

Suggested change

	assert multiplied_safe_buffer.html_safe?
	assert_predicate multiplied_safe_buffer, :html_safe?

[kamipo]

Suggested change

	assert_not multiplied_unsafe_buffer.html_safe?
	assert_not_predicate multiplied_unsafe_buffer, :html_safe?

[r7kamura]

Thanks. I rewrote the test code and added an entry to CHANGELOG.

[kamipo]

Thanks!