Update primary constructor for PaymentOption.

[jaynewstrom-stripe]

Summary

Follow up to https://github.com/stripe/stripe-android/pull/8436 which makes all the properties val instead of var. The only downside to this is the change to the generated copy method. Which we've deemed fine in other cases, so I think it's fine here too.

[github-actions[bot]]

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 │   4.3 MiB │   4.3 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 │   8.1 KiB │   8.1 KiB │  0 B 
      res │ 301.5 KiB │ 301.5 KiB │  0 B │   455 KiB │   455 KiB │  0 B 
   native │   7.3 MiB │   7.3 MiB │  0 B │  18.4 MiB │  18.4 MiB │  0 B 
    asset │   1.5 MiB │   1.5 MiB │  0 B │   1.5 MiB │   1.5 MiB │  0 B 
    other │    87 KiB │    87 KiB │ +2 B │ 161.5 KiB │ 161.5 KiB │  0 B 
──────────┼───────────┼───────────┼──────┼───────────┼───────────┼──────
    total │  12.2 MiB │  12.2 MiB │ +2 B │  25.8 MiB │  25.8 MiB │  0 B 

 DEX     │ old   │ new   │ diff      
─────────┼───────┼───────┼───────────
   files │     1 │     1 │ 0         
 strings │ 21686 │ 21686 │ 0 (+0 -0) 
   types │  6869 │  6869 │ 0 (+0 -0) 
 classes │  5634 │  5634 │ 0 (+0 -0) 
 methods │ 31447 │ 31447 │ 0 (+0 -0) 
  fields │ 18315 │ 18315 │ 0 (+0 -0) 

 ARSC    │ old  │ new  │ diff 
─────────┼──────┼──────┼──────
 configs │  164 │  164 │  0   
 entries │ 3404 │ 3404 │  0

APK

   compressed    │   uncompressed   │                        
──────────┬──────┼───────────┬──────┤                        
 size     │ diff │ size      │ diff │ path                   
──────────┼──────┼───────────┼──────┼────────────────────────
  1.2 KiB │ +3 B │   1.2 KiB │  0 B │ ∆ META-INF/CERT.RSA    
 25.9 KiB │ -3 B │  63.9 KiB │  0 B │ ∆ META-INF/MANIFEST.MF 
 29.1 KiB │ +2 B │    64 KiB │  0 B │ ∆ META-INF/CERT.SF     
──────────┼──────┼───────────┼──────┼────────────────────────
 56.1 KiB │ +2 B │ 129.1 KiB │  0 B │ (total)