Move logic into the interactor.

[jaynewstrom-stripe]

Summary

I plan to share this logic in embedded, and I don't plan to use PaymentSheetScreen.

This is a pure refactor to take advantage of in a follow up.

[github-actions]

Diffuse output:

OLD: identity-example-release-base.apk (signature: V1, V2)
NEW: identity-example-release-pr.apk (signature: V1, V2)

          │          compressed          │         uncompressed         
          ├───────────┬───────────┬──────┼───────────┬───────────┬──────
 APK      │ old       │ new       │ diff │ old       │ new       │ diff 
──────────┼───────────┼───────────┼──────┼───────────┼───────────┼──────
      dex │     2 MiB │     2 MiB │  0 B │   4.1 MiB │   4.1 MiB │  0 B 
     arsc │     1 MiB │     1 MiB │  0 B │     1 MiB │     1 MiB │  0 B 
 manifest │   2.3 KiB │   2.3 KiB │  0 B │     8 KiB │     8 KiB │  0 B 
      res │ 302.6 KiB │ 302.6 KiB │  0 B │ 456.7 KiB │ 456.7 KiB │  0 B 
   native │   6.2 MiB │   6.2 MiB │  0 B │  15.8 MiB │  15.8 MiB │  0 B 
    asset │   7.1 KiB │   7.1 KiB │  0 B │   6.9 KiB │   6.9 KiB │  0 B 
    other │  90.4 KiB │  90.4 KiB │ +9 B │ 170.7 KiB │ 170.7 KiB │  0 B 
──────────┼───────────┼───────────┼──────┼───────────┼───────────┼──────
    total │   9.6 MiB │   9.6 MiB │ +9 B │  21.5 MiB │  21.5 MiB │  0 B 

 DEX     │ old   │ new   │ diff      
─────────┼───────┼───────┼───────────
   files │     1 │     1 │ 0         
 strings │ 19975 │ 19975 │ 0 (+0 -0) 
   types │  6193 │  6193 │ 0 (+0 -0) 
 classes │  4985 │  4985 │ 0 (+0 -0) 
 methods │ 29820 │ 29820 │ 0 (+0 -0) 
  fields │ 17538 │ 17538 │ 0 (+0 -0) 

 ARSC    │ old  │ new  │ diff 
─────────┼──────┼──────┼──────
 configs │  164 │  164 │  0   
 entries │ 3624 │ 3624 │  0

APK

   compressed    │  uncompressed   │                                           
──────────┬──────┼──────────┬──────┤                                           
 size     │ diff │ size     │ diff │ path                                      
──────────┼──────┼──────────┼──────┼───────────────────────────────────────────
 28.5 KiB │ +9 B │ 63.1 KiB │  0 B │ ∆ META-INF/CERT.SF                        
    272 B │ +1 B │    120 B │  0 B │ ∆ META-INF/version-control-info.textproto 
  1.2 KiB │ -1 B │  1.2 KiB │  0 B │ ∆ META-INF/CERT.RSA                       
──────────┼──────┼──────────┼──────┼───────────────────────────────────────────
   30 KiB │ +9 B │ 64.4 KiB │  0 B │ (total)