FIX: Use named params correctly with dir-span (PR #14203)

Follow up to: a2ccf0a9ff22f3e8467ac0d61f93be136bb66b31

These named params need to be passed in as strings.

With htmlSafe=true the params show up as {}, but with htmlSafe="true", the params show up as {"htmlSafe":"true"}

Bug reported here: Topic excerpt html issue - bug - Discourse Meta


Looks good to me but maybe @eviltrout who is better with Ember can review this time.

I thought this when I reviewed the previous one and was surprised it worked!

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