Add double end arrow to gizmos

[pablo-lua]

Objective

• Implement double ended arrows, suggestion of Tracking issue: Amazing Gizmos #9400

Solution

• Creation of new field and method to the ArrowBuilder

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Changelog

Added

• New field ArrowBuilder::double_ended
• New method ArrowBuilder::with_double_end to redefine the double_ended field

Additional

I added this in the 3d_gizmos example, that's the result:

I added this arrow in the 2d_gizmos example too:

[afonsolage]

The code seems fine, only small changes and I think the 3d example doesn't showcase well the double ended gizmos.

[pablo-lua]

I changed the arrow position in the example, it is like the image now.