Remove redundant non-trivial Variant types initializations

[Sauermann]

As mentioned in #68627 (comment).

[akien-mga]

While at it, there's also:

scene/resources/skeleton_modification_2d_fabrik.h
71:     Transform2D target_global_pose = Transform2D();
72:     Transform2D origin_global_pose = Transform2D();

And some more for other types, e.g. Transform3D:

$ rg "Transform3D .* = Transform3D\(\);" --sort path
core/variant/variant_call.cpp
2441:   Transform3D identity_transform = Transform3D();

drivers/gles3/rasterizer_scene_gles3.h
102:    Transform3D cam_transform = Transform3D();
103:    Transform3D inv_cam_transform = Transform3D();

editor/plugins/node_3d_editor_plugin.cpp
3495:           Transform3D axis_angle = Transform3D();

editor/plugins/skeleton_3d_editor_plugin.cpp
1291:   Transform3D original_to_local = Transform3D();
1299:   Transform3D t = Transform3D();

scene/resources/skeleton_modification_3d_fabrik.h
71:     Transform3D target_global_pose = Transform3D();
72:     Transform3D origin_global_pose = Transform3D();

And all other non-trivial Variant types such as Vector*, String, Color, StringName, etc. all have similar occurrences. But I guess that's out of scope for this PR :)

[Sauermann]

And all other non-trivial Variant types such as Vector*, String, Color, StringName, etc. all have similar occurrences. But I guess that's out of scope for this PR :)

I can simply rename the PR to "Remove redundant initialization" to change the scope ;-)
Will see what I can find.

[Sauermann]

Initializing a String with StringName() was probably not intentional.

[akien-mga]

Thanks!