resolve alpha button override issues in configuration

[mojganii]

The issue was that the AppButton was messing with the button's alpha when switching between normal and disabled states to keep a nice look for the disabled mode. At the same time, the disconnectButton was getting shown and hidden using its alpha value. This conflicts in how we were handling alpha values caused the problem.

To fix it, I added a function that creates a new image with the opacity for the UIButton's background. Now, I apply the alpha to that image instead of changing the UIButton's alpha directly.

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This change is 

[linear]

IOS-888 Disconnect button appears when no time left on the device

[rablador]

The text on disabled buttons is very dark. Can we make it a bit more visible?

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @mojganii)

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ios/MullvadVPN/Extensions/UIImage+Helpers.swift line 30 at r1 (raw file):

    }

    func withAlpha(_ alpha: CGFloat) -> UIImage? {

This can be reduced a bit, eg:

Code snippet:

func withAlpha(_ alpha: CGFloat) -> UIImage {
    return UIGraphicsImageRenderer(size: size, format: imageRendererFormat).image { _ in
        draw(in: CGRect(origin: .zero, size: size), blendMode: .normal, alpha: alpha)
    }
}

[mojganii]

Reviewable status: 2 of 5 files reviewed, 1 unresolved discussion (waiting on @rablador)

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ios/MullvadVPN/Extensions/UIImage+Helpers.swift line 30 at r1 (raw file):

Previously, rablador (Jon Petersson) wrote…

This can be reduced a bit, eg:

interesting!

[rablador]

Reviewed 3 of 3 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved

[mojganii]

I think the text color for the disabled state is already enough to make it distinguish for disabled state. I personally prefer to remove alpha from that. the text color for Delete Account is lightGray for the left image and the value for the right image is light gray with 0.5 alpha value.

Reviewable status: complete! all files reviewed, all discussions resolved

[buggmagnet]

Reviewed 2 of 5 files at r1, 3 of 3 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved

[github-actions]

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