Add setup_future_usage for saved Link payment methods from PM and passthrough mode.

[samer-stripe]

Summary

Add setup_future_usage for saved payment methods from PM and passthrough mode.

Currently, we assume that paying with saved payment methods (using PaymentMethod objects) meant that the payment method was already attached to the customer. We recently found out that Link was not saving payment methods to the customer account due to a limitation from the Mobile SDK's continued usage of ephemeral keys over customer sessions.

This PR adds behavior for allowing payment methods saved on Link to also be saved on the customer's account so that they can be reused by the customer through Elements UI interfaces as well as expected when the customer asks to save a payment method through PaymentSheet.

When we move to CustomerSession, Link will automatically save the payment method on both Link and their Stripe customer's account rather than need to implement a solution on the client side.

Motivation

Fixes an issue in passthrough mode where a payment method saved through Link signup is not saved in as a customer payment method.

Testing

• Added tests
• Modified tests
• Manually verified

[github-actions]

Diffuse output:

OLD: paymentsheet-example-release-master.apk (signature: V1, V2)
NEW: paymentsheet-example-release-pr.apk (signature: V1, V2)

          │           compressed           │          uncompressed          
          ├───────────┬───────────┬────────┼───────────┬───────────┬────────
 APK      │ old       │ new       │ diff   │ old       │ new       │ diff   
──────────┼───────────┼───────────┼────────┼───────────┼───────────┼────────
      dex │   3.9 MiB │   3.9 MiB │ +283 B │   8.6 MiB │   8.6 MiB │ +568 B 
     arsc │   2.2 MiB │   2.2 MiB │    0 B │   2.2 MiB │   2.2 MiB │    0 B 
 manifest │   5.1 KiB │   5.1 KiB │    0 B │  25.4 KiB │  25.4 KiB │    0 B 
      res │ 911.1 KiB │ 911.1 KiB │    0 B │   1.4 MiB │   1.4 MiB │    0 B 
   native │   2.6 MiB │   2.6 MiB │    0 B │     6 MiB │     6 MiB │    0 B 
    asset │     3 MiB │     3 MiB │  +13 B │     3 MiB │     3 MiB │  +13 B 
    other │ 204.2 KiB │ 204.3 KiB │   +8 B │ 445.3 KiB │ 445.3 KiB │    0 B 
──────────┼───────────┼───────────┼────────┼───────────┼───────────┼────────
    total │  12.8 MiB │  12.8 MiB │ +304 B │  21.7 MiB │  21.7 MiB │ +581 B 

 DEX     │ old   │ new   │ diff       
─────────┼───────┼───────┼────────────
   files │     1 │     1 │  0         
 strings │ 42698 │ 42699 │ +1 (+2 -1) 
   types │ 14592 │ 14592 │  0 (+0 -0) 
 classes │ 12341 │ 12341 │  0 (+0 -0) 
 methods │ 60861 │ 60862 │ +1 (+7 -6) 
  fields │ 40030 │ 40033 │ +3 (+8 -5) 

 ARSC    │ old  │ new  │ diff 
─────────┼──────┼──────┼──────
 configs │  242 │  242 │  0   
 entries │ 6029 │ 6029 │  0

APK

    compressed     │    uncompressed    │                                           
──────────┬────────┼───────────┬────────┤                                           
 size     │ diff   │ size      │ diff   │ path                                      
──────────┼────────┼───────────┼────────┼───────────────────────────────────────────
  3.9 MiB │ +283 B │   8.6 MiB │ +568 B │ ∆ classes.dex                             
  7.3 KiB │  +13 B │   7.2 KiB │  +13 B │ ∆ assets/dexopt/baseline.prof             
 62.1 KiB │   +9 B │   140 KiB │    0 B │ ∆ META-INF/CERT.SF                        
  1.2 KiB │   -3 B │   1.2 KiB │    0 B │ ∆ META-INF/CERT.RSA                       
 53.2 KiB │   +3 B │ 139.9 KiB │    0 B │ ∆ META-INF/MANIFEST.MF                    
    271 B │   -1 B │     120 B │    0 B │ ∆ META-INF/version-control-info.textproto 
──────────┼────────┼───────────┼────────┼───────────────────────────────────────────
    4 MiB │ +304 B │   8.8 MiB │ +581 B │ (total)

DEX

STRINGS:

   old   │ new   │ diff       
  ───────┼───────┼────────────
   42698 │ 42699 │ +1 (+2 -1) 
  
  + , requiresSaveOnConfirmation=
  + ~~R8{backend:dex,compilation-mode:release,has-checksums:false,min-api:21,pg-map-id:7b7a6e8,r8-mode:full,version:8.3.37}
  
  - ~~R8{backend:dex,compilation-mode:release,has-checksums:false,min-api:21,pg-map-id:e983f41,r8-mode:full,version:8.3.37}
  

METHODS:

   old   │ new   │ diff       
  ───────┼───────┼────────────
   60861 │ 60862 │ +1 (+7 -6) 
  
  + B4.b z(W0, boolean) → p
  + B4.c z(W0, boolean) → p
  + F6.M a(j, l1, m, boolean, e) → Object
  + K7.f z(W0, boolean) → p
  + e7.s <init>(n, m)
  + e7.y <init>(W0, w, int)
  + e7.y <init>(W0, w, boolean)
  
  - B4.b z(W0) → p
  - B4.c z(W0) → p
  - F6.M a(j, l1, boolean, e) → Object
  - K7.f z(W0) → p
  - e7.s <init>(n)
  - e7.y <init>(W0, w)
  

FIELDS:

   old   │ new   │ diff       
  ───────┼───────┼────────────
   40030 │ 40033 │ +3 (+8 -5) 
  
  + F6.H W: m
  + F6.H X: Object
  + F6.H Y: M
  + F6.H Z: int
  + e7.s V: p1
  + e7.s W: int
  + e7.s X: String
  + e7.y U: boolean
  
  - F6.H W: Object
  - F6.H X: M
  - F6.H Y: int
  - e7.s V: int
  - e7.s W: String

[jaynewstrom-stripe]

Do we have tests for passing the right value into this?

[samer-stripe]

Added some network tests for ensuring the value is properly passed in PM and passthrough mode.

[jaynewstrom-stripe]

Is it possible to have unit tests as well?

[samer-stripe]

Added unit tests in PaymentSheetViewModel.

[amk-stripe]

can you add something to the description about what the new behavior is? I think we discussed this a bit in a call last week and one of the possible fixes leads to duplicate payment methods showing up in some cases. It'd be nice to know if that's this fix and how this fix works

[jaynewstrom-stripe]

Is it possible to have unit tests as well?

[amk-stripe]

are there existing tests for a different PaymentSelection.CustomerRequestedSave option for FlowController?

[samer-stripe]

The logic for this actual is handled inside its PaymentSheet variant view model PaymentOptionsViewModel. Added some tests there.