The `Add` > `Scene` > `New Scene` operator was behaving as follows:
* If there is no active scene strip, create an empty blank scene and
assign it to a new scene strip.
* Otherwise, use the scene referenced by the active scene strip and
use one of the copy scene methods (blank, copy settings, copy linked,
or full copy) to create a new scene and assign it to a
new scene strip.
This was not ideal for 2 reasons:
1. With no strip selected, creating blank scenes is generally not very
useful as it means that the user has to e.g. update all the render
settings, add a camera, etc.
2. The behavior of copying an existing scene by using the active strip
is very hidden. Also because adding the strip immedialty calls the
move operator, so you cannot even adjust the copy method of the
scene.
This PR changes 3 things:
1. Don't use at the active scene strip. Instead use the active scene.
2. Don't create an empty blank scene, copy the settings of the active
scene by default. This means that e.g. render settings can be reused.
3. The operator entry in the `Add` > `Scene` menu is now called `Empty Scene`.
Part of #144063.
Pull Request: https://projects.blender.org/blender/blender/pulls/144069
816da3c63b