Display iOS QR Code feature on Desktop

[bsclifton]

Test plan

1. New profile
2. Visit brave://rewards/
3. Verify QR code button is showing
4. Follow steps in official help article https://support.brave.com/hc/en-us/articles/360052811072

Description

There was an issue with transfers between iOS and Desktop which has been identified and is being fixed. After this is resolved, we need to re-introduce the QR code

History of QR code (for posterity)

1. Originally introduced with Add QR code for iOS to scan #12176
2. Hidden with Hide iOS QR Code function in Rewards Settings #12475 because iOS side was not ready at the time
3. Shown again with Display iOS QR Code feature once on Desktop when iOS v1.22 is released  #12476, targeting the 1.18 release
4. Hidden after encountering an issue with Hide iOS QR Code function in Rewards Settings #13053 which shipped with 1.18

[LaurenWags]

Verified passed with

Brave | 1.18.75 Chromium: 87.0.4280.101 (Official Build) (x86_64)
-- | --
Revision | 9407c80213cda69c2b7abcb4fa8e3f74488f4956-refs/branch-heads/4280@{#1807}
OS | macOS Version 10.15.7 (Build 19H15)

Verified the following:

1. Clean install, scan QR code and confirm it matches paymentId on brave://rewards-internals
2. Close/relaunch browser
3. Scan QR code and confirm it matches paymentId on brave://rewards-internals
4. Restore a wallet
5. Scan QR code and confirm it is updated and matches paymentId on brave://rewards-internals
6. Close/relaunch browser
7. Scan QR code and confirm it is updated and matches paymentId on brave://rewards-internals

Additionally, confirmed toggling ads on/off and AC on/off did not affect paymentId/QR code.

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Verification passed on

Brave	1.18.75 Chromium: 87.0.4280.101 (Official Build) (64-bit)
Revision	9407c80213cda69c2b7abcb4fa8e3f74488f4956-refs/branch-heads/4280@{#1807}
OS	Ubuntu 18.04 LTS

Verified the above test plan

---

Verification passed on

Brave	1.18.75 Chromium: 87.0.4280.101 (Official Build) (64-bit)
Revision	9407c80213cda69c2b7abcb4fa8e3f74488f4956-refs/branch-heads/4280@{#1807}
OS	Windows 7 Service Pack 1 (Build 7601.24544)

Verified the above test plan