cli/save-as: update to handle format elements

[anGie44]

Closes #2442

Manually tested with:
a)

aseprite -b $PATH/Sprite-0001.ase --save-as '{title}.png'

Output: Sprite-0001.png

b)

aseprite -b $PATH/Sprite-0001.ase --save-as 'a-{title}-b.png'

Output: a-Sprite-0001-b.png

[dacap]

Hi @anGie44 thanks for this patch, could you please check the CLA signing process?

[anGie44]

all set @dacap 👍

[dacap]

I've tested this patch with a sprite with several frames doing

aseprite -b animation.aseprite -save-as "{title}.png"

and all frames are saved in the same file animation.png. Anyway in previous versions the saved file are {title}1.png, {title}2.png, etc. while the best output would be animation1.png, animation2.png, etc.

I have to oreview this patch and probably merge it with other fixes to avoid breaking some other cases.

[dacap]

Thanks a lot @anGie44, I've just merged this PR (it was automatically closed in the past when we deleted the master branch, now we use the main branch).

I've added to support saving multiple files with one -save-as too, as requested in #2442