Add quantum resistance settings to preferences view if DEBUG is set

[acb-mv]

This adds a "Quantum resistance" menu to the VPN options with three modes: On, Off and Automatic. It is disabled if DEBUG is not set.

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This change is 

[linear]

IOS-459 Add quantum-resistant option to settings

[buggmagnet]

Reviewed 6 of 8 files at r1, 2 of 2 files at r2, all commit messages.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @acb-mv)

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ios/MullvadVPN/View controllers/Preferences/PreferencesDataSource.swift line 530 at r2 (raw file):

            "QUANTUM_RESISTANCE_HEADER_LABEL",
            tableName: "Preferences",
            value: "Quantum Resistance",

Usually we try to have the same copy on all the platforms, following what Desktop wrote in most cases.

This should be titled "Quantum-resistant tunnel"

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ios/MullvadVPN/View controllers/Preferences/PreferencesInteractor.swift line 59 at r2 (raw file):

    }

    func setQuantumResistance(_ newSetting: TunnelQuantumResistance) {

That function was defined but is never used

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ios/MullvadVPN/View controllers/Preferences/PreferencesViewController.swift line 160 at r2 (raw file):

                tableName: "QuantumResistance",
                value: """
                Text on quantum resistance goes here.

The text should say

This feature makes the WireGuard tunnel resistant to potential attacks from quantum computers.
It does this by performing an extra key exchange using a quantum safe algorithm and mixing the result into WireGuard’s regular encryption.
This extra step uses approximately 500 kiB of traffic every time a new tunnel is established.

[acb-mv]

Reviewable status: 6 of 8 files reviewed, 3 unresolved discussions (waiting on @buggmagnet)

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ios/MullvadVPN/View controllers/Preferences/PreferencesDataSource.swift line 530 at r2 (raw file):

Previously, buggmagnet wrote…

Usually we try to have the same copy on all the platforms, following what Desktop wrote in most cases.

This should be titled "Quantum-resistant tunnel"

Done.

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ios/MullvadVPN/View controllers/Preferences/PreferencesInteractor.swift line 59 at r2 (raw file):

Previously, buggmagnet wrote…

That function was defined but is never used

Done.

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ios/MullvadVPN/View controllers/Preferences/PreferencesViewController.swift line 160 at r2 (raw file):

Previously, buggmagnet wrote…

The text should say

This feature makes the WireGuard tunnel resistant to potential attacks from quantum computers.
It does this by performing an extra key exchange using a quantum safe algorithm and mixing the result into WireGuard’s regular encryption.
This extra step uses approximately 500 kiB of traffic every time a new tunnel is established.

Done.

[buggmagnet]

Reviewed 2 of 2 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved