Added option to set scaler and filter

[Root-Core]

One of my friends rage-uninstalled Linux as he wasn't able to set his shooter to a streched resolution.
Therefore I want to prevent other people from suffering that much and made the already existing option accessible.

As it was superfluous, I removed the option to explicitly force integer scaler. This might be a breaking change.

Some points to discuss:

• Shouldn't we do the same for the upscaler filter?
  At the moment there are multiple options that contradict each other. (-U, -Y, -n)
• On my machine the README.md isn't correct about building instructions as the binary is at build/src/gamescope.
  Is this a mistake?
• I thought about implementing shortcuts to cycle through the scalers / filters.
  Would this be useful to anybody or would explicit shortcuts make more sense?

Related: #399

[misyltoad]

If we are changing this, lets do it for the filter as well.

I agree that we are probably long-ish due for changing the key binds for these too to cycle instead of toggle.

It's a breaking change but I don't think it's world breaking unlike if we changed what atoms used etc.

[Root-Core]

If we are changing this, lets do it for the filter as well.

Should I implement that change? If anything, the number of options will only increase as more upscalers come out.

I agree that we are probably long-ish due for changing the key binds for these too to cycle instead of toggle.

I have implemented a shortcut for this already on my machine, but you do not know which one is currently selected. There is no output / overlay. We could communicate it with MangoApp.

It's a breaking change but I don't think it's world breaking unlike if we changed what atoms used etc.

Sure, I think the changes in this PR will not affect many people and it is fairly easy to adopt.

[misyltoad]

Go for it :)

[Ichicoro]

Thanks, I managed to compile this PR and I can finally play stretched CS:GO in desktop mode on my Deck without having to change the desktop resolution :)

[keybangz]

Compiled this PR and works well playing CSGO on my laptop. 1440x1080p on Wayland with -vulkan

Did try and get it working with flatpak steam however it complained Xwayland couldn't be found (I couldn't figure it out for the life of me, maybe someone smarter will)

CPU: 11th Gen Intel i7-11370H (8) @ 4.800GHz
GPU: NVIDIA GeForce RTX 3060 Mobile / Max-Q

[Root-Core]

@Ichicoro @cigzag I'm happy it worked out for you. ;)

@cigzag Regarding your issue, have a look at #848. This sounds like it matches your use case. I think you are using a hybrid gpu setup?

@Joshua-Ashton I also have implemented the argument for the filters, is anything holding back this PR?
Please also have a look at #895.