fix rtl image spacing

[JillianK]

In removing spacing from PaneButtons that don't have icons as part of this change, I removed the spacing between RTL PaneButtons that use the hiddenImage property instead of the iconClass property to set the icon in the button. This adds a check on the hiddenImage property before removing icon padding.

From the eyes test, the show blocks button here is an example of the issue

Here's the fixed version on show blocks

PR Checklist:

• Tests provide adequate coverage
• Privacy and Security impacts have been assessed
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

[breville]

Thanks for the fix!