Allow users to pass --enable/disable-features flag

[takase1121]

This PR implements the solution in #526.

I am also looking to adding the flags to Vesktop, unfortunately it is impossible to set the argument in time as app.getGPUInfo() is async and I don't know if Electron has already initialized the GUI backend by then. It might be worth looking into as a toggle in the settings (probably something like "Experimental Video Decode Acceleration on AMD" but this is so specific it's hard to come out with a suitable name).

[Vendicated]

this is meh. if the user wants to override one switch, it will disable everything else

why not merge our switches into the user switches? could do the same for disable-features

const features = app.commandLine.getSwitchValue("enable-features").split(",");
features.push("Feature1", "Feature2");

app.commandLine.appendSwitch("enable-features", [...new Set(features)].filter(Boolean).join(","));

[takase1121]

this is meh. if the user wants to override one switch, it will disable everything else

why not merge our switches into the user switches? could do the same for disable-features

const features = app.commandLine.getSwitchValue("enable-features").split(",");
features.push("Feature1", "Feature2");

app.commandLine.appendSwitch("enable-features", [...new Set(features)].filter(Boolean).join(","));

That would be an option. I'm just mainly concerned with conflicting switches.m, but I think it will probably be fine.

[takase1121]

I'm just mainly concerned with conflicting switches.m, but I think it will probably be fine.

This might not be an issue at all. When a flag appears in both enable-features and disable-features, it will be disabled. If someone wants to override Vesktop's flags, they can just disable them from the CLI. Assuming Vesktop doesn't disable something crazy by default (right not it doesn't) this will work well.

P.S.: Is this something worth documenting?

[Vendicated]

thank you!