Ruby

Make encoding loading not issue warning

Instead of relying on setting an unsetting ruby_verbose, which is
not thread-safe, restructure require_internal and load_lock to
accept a warn argument for whether to warn, and add
rb_require_internal_silent to require without warnings. Use
rb_require_internal_silent when loading encoding.

Note this does not modify ruby_debug and errinfo handling, those
remain thread-unsafe.

Also silent requires when loading transcoders.