Make things that do work happen on the work context in view models.

[jaynewstrom-stripe]

Summary

I was digging into some test flakes, and I noticed that CustomerSheet was SUPER janky on confirm. We were moving things to corountines via viewModelScope.launch. Unfortunately we weren't actually switching off the main thread. Where we're actually doing work that needs to be off the main thread, we should move it!

[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 │   4.2 MiB │   4.2 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 │   1.6 MiB │   1.6 MiB │  0 B │   1.6 MiB │   1.6 MiB │  0 B 
    other │  99.8 KiB │  99.8 KiB │ +4 B │ 206.8 KiB │ 206.8 KiB │  0 B 
──────────┼───────────┼───────────┼──────┼───────────┼───────────┼──────
    total │  12.3 MiB │  12.3 MiB │ +4 B │  25.8 MiB │  25.8 MiB │  0 B 

 DEX     │ old   │ new   │ diff      
─────────┼───────┼───────┼───────────
   files │     1 │     1 │ 0         
 strings │ 21468 │ 21468 │ 0 (+0 -0) 
   types │  6635 │  6635 │ 0 (+0 -0) 
 classes │  5401 │  5401 │ 0 (+0 -0) 
 methods │ 30994 │ 30994 │ 0 (+0 -0) 
  fields │ 18075 │ 18075 │ 0 (+0 -0) 

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

APK

   compressed    │   uncompressed   │                        
──────────┬──────┼───────────┬──────┤                        
 size     │ diff │ size      │ diff │ path                   
──────────┼──────┼───────────┼──────┼────────────────────────
 38.2 KiB │ +4 B │  86.7 KiB │  0 B │ ∆ META-INF/CERT.SF     
  1.2 KiB │ -1 B │   1.2 KiB │  0 B │ ∆ META-INF/CERT.RSA    
 29.5 KiB │ +1 B │  86.6 KiB │  0 B │ ∆ META-INF/MANIFEST.MF 
──────────┼──────┼───────────┼──────┼────────────────────────
 68.9 KiB │ +4 B │ 174.5 KiB │  0 B │ (total)