Make payment method serializable.

[jaynewstrom-stripe]

Summary

Fixes #7827

This was causing issues when serializing PaymentSheetLoadingException.PaymentIntentInTerminalState.
Originally introduced in #7704

[jaynewstrom-stripe]

I think the right fix is actually ripping out PaymentMethod from PaymentSheetLoadingException.

[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 │ +229 B │   8.5 MiB │   8.5 MiB │ +36 B 
     arsc │   2.4 MiB │   2.4 MiB │    0 B │   2.4 MiB │   2.4 MiB │   0 B 
 manifest │   5.1 KiB │   5.1 KiB │    0 B │  25.4 KiB │  25.4 KiB │   0 B 
      res │ 967.5 KiB │ 967.5 KiB │    0 B │   1.5 MiB │   1.5 MiB │   0 B 
   native │   2.6 MiB │   2.6 MiB │    0 B │     6 MiB │     6 MiB │   0 B 
    asset │     3 MiB │     3 MiB │   +1 B │     3 MiB │     3 MiB │  +1 B 
    other │ 211.2 KiB │ 211.2 KiB │   +1 B │ 471.8 KiB │ 471.8 KiB │   0 B 
──────────┼───────────┼───────────┼────────┼───────────┼───────────┼───────
    total │    13 MiB │    13 MiB │ +231 B │  21.9 MiB │  21.9 MiB │ +37 B 

 DEX     │ old   │ new   │ diff      
─────────┼───────┼───────┼───────────
   files │     1 │     1 │ 0         
 strings │ 42394 │ 42394 │ 0 (+1 -1) 
   types │ 14381 │ 14381 │ 0 (+0 -0) 
 classes │ 12182 │ 12182 │ 0 (+0 -0) 
 methods │ 60034 │ 60034 │ 0 (+1 -1) 
  fields │ 39649 │ 39649 │ 0 (+1 -1) 

 ARSC    │ old  │ new  │ diff 
─────────┼──────┼──────┼──────
 configs │  328 │  328 │  0   
 entries │ 7262 │ 7262 │  0

APK

    compressed     │   uncompressed    │                               
──────────┬────────┼───────────┬───────┤                               
 size     │ diff   │ size      │ diff  │ path                          
──────────┼────────┼───────────┼───────┼───────────────────────────────
  3.9 MiB │ +229 B │   8.5 MiB │ +36 B │ ∆ classes.dex                 
   68 KiB │   +2 B │ 153.3 KiB │   0 B │ ∆ META-INF/CERT.SF            
  7.2 KiB │   +1 B │   7.1 KiB │  +1 B │ ∆ assets/dexopt/baseline.prof 
 54.5 KiB │   -1 B │ 153.2 KiB │   0 B │ ∆ META-INF/MANIFEST.MF        
──────────┼────────┼───────────┼───────┼───────────────────────────────
    4 MiB │ +231 B │   8.8 MiB │ +37 B │ (total)

DEX

STRINGS:

   old   │ new   │ diff      
  ───────┼───────┼───────────
   42394 │ 42394 │ 0 (+1 -1) 
  + ~~R8{backend:dex,compilation-mode:release,has-checksums:false,min-api:21,pg-map-id:c9f168e,r8-mode:full,version:8.2.47}
  
  - ~~R8{backend:dex,compilation-mode:release,has-checksums:false,min-api:21,pg-map-id:3c46251,r8-mode:full,version:8.2.47}
  

METHODS:

   old   │ new   │ diff      
  ───────┼───────┼───────────
   60034 │ 60034 │ 0 (+1 -1) 
  + dh.x1 <init>(Object, Serializable, int)
  
  - dh.x1 <init>(int, Object, Object)
  

FIELDS:

   old   │ new   │ diff      
  ───────┼───────┼───────────
   39649 │ 39649 │ 0 (+1 -1) 
  + dh.x1 T: Serializable
  
  - dh.x1 T: Object