frontend: Copy show/hide transitions when pasting source as duplicate

[howellrl]

Description

When a source is copied and pasted as duplicate, copy the show and hide transitions onto the newly created scene item.

Motivation and Context

This fixes #11192 - Show/Hide transitions don't copy when duplicating a source. The ticket describes an issue where copying a source and pasting as duplicate does not bring the show and hide transitions to the pasted item.

How Has This Been Tested?

Tested on Windows 11

Ran OBS Studio before making changes. Followed recreation steps in issue and observed described behavior. Transitions were not being copied.

Made changes, ran OBS Studio and followed recreation steps. Transitions are now copied.

• Tested Text (GDI+), Image, Window Capture sources.
• Tested Fade and Swipe transitions.
• Verified show and hide transitions were both copied.
• Made changes to source after pasting to confirm the changes did not affect the duplicate - this verified that transitions were duplicated and not referenced.
• Verified paste as reference was not affected. Paste as reference was not called out in the ticket.
• Tested undo/redo of paste, transitions were still present on duplicate.
• After copy and paste, restarted OBS, transitions were still present on duplicate.

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.