[connect] Update background and loading spinner colors

[lng-stripe]

Summary

Per stripe/stripe-ios#4140

• Update the WebView background color to be the appearance background color, or (if unset) white.
• Update the native loading spinner color to be the appearance secondary text color, or (if unset) a color sufficiently contrast against the background color.

Motivation

https://jira.corp.stripe.com/browse/MXMOBILE-2744

Testing

• Added tests
• Modified tests
• Manually verified

Screenshots

Screen.Recording.2024-11-19.at.4.57.36.PM-compressed.mov

[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 │ 301.8 KiB │ 301.8 KiB │  0 B │ 455.5 KiB │ 455.5 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 │  90.2 KiB │  90.2 KiB │ -2 B │ 170.3 KiB │ 170.3 KiB │  0 B 
──────────┼───────────┼───────────┼──────┼───────────┼───────────┼──────
    total │   9.6 MiB │   9.6 MiB │ -2 B │  21.5 MiB │  21.5 MiB │  0 B 

 DEX     │ old   │ new   │ diff      
─────────┼───────┼───────┼───────────
   files │     1 │     1 │ 0         
 strings │ 19966 │ 19966 │ 0 (+0 -0) 
   types │  6188 │  6188 │ 0 (+0 -0) 
 classes │  4979 │  4979 │ 0 (+0 -0) 
 methods │ 29759 │ 29759 │ 0 (+0 -0) 
  fields │ 17526 │ 17526 │ 0 (+0 -0) 

 ARSC    │ old  │ new  │ diff 
─────────┼──────┼──────┼──────
 configs │  164 │  164 │  0   
 entries │ 3622 │ 3622 │  0

APK

   compressed    │  uncompressed   │                        
──────────┬──────┼──────────┬──────┤                        
 size     │ diff │ size     │ diff │ path                   
──────────┼──────┼──────────┼──────┼────────────────────────
  1.2 KiB │ -1 B │  1.2 KiB │  0 B │ ∆ META-INF/CERT.RSA    
 25.3 KiB │ -1 B │ 62.8 KiB │  0 B │ ∆ META-INF/MANIFEST.MF 
──────────┼──────┼──────────┼──────┼────────────────────────
 26.5 KiB │ -2 B │ 64.1 KiB │  0 B │ (total)