[PAY-1816] Payment Sheet Loading States

[msadoon]

📲 What

Before and after the "New Payment Method" button is tapped we have a lag that is time taken during network requests from our end before Stripe's payment sheet is displayed.

Let's inform the user that he/she needs to wait before seeing the new UI/UX, and

🤔 Why

It's good to let the user understand there is a waiting period before we eventually update the UI/UX with the data from Stripe's payment sheet.

🛠 How

PledgePaymentMethodAddCell gets a loading state with an ActivityIndicator.
PledgePaymentMethodsDataSource gets a state to turn on/check loading for the above cell.
PledgeViewController gets a delegate to cancel appearance of payment sheet if the user pledges/clicks TOS/presents other views. User cannot click on "Add new card" until its out of its loading state.
PledgeViewModel gets a shouldCancelPaymentSheetAppearance signal that is triggered whenever the above delegate method is called, also internally when new cards are selected and if there is an error on PledgePaymentMethodsViewController.

👀 See

Before 🐛

Simulator.Screen.Recording.-.iPhone.8.-.2022-08-24.at.10.29.19.mp4

After 🦋

Simulator.Screen.Recording.-.iPhone.8.-.2022-08-24.at.10.21.29.mp4

✅ Acceptance criteria

• Loading state appears before payment sheet is shown
• Loading state continues to appear until payment method/error/payment sheet closed.

⏰ TODO

• Ensure no duplicate taps occur when tapping the "Add New Payment" button
• Ensure that loading spinner stops spinning when either error/payment card added.
• Ensure selecting a new card stops showing of payment sheet.
• Ensure pledging can occur during loading state (regular and Apple Pay)
• Write tests.

[codecov]

Codecov Report

Merging #1713 (03b93ca) into main (8ccf0b4) will increase coverage by 0.01%.
The diff coverage is 90.90%.

@@            Coverage Diff             @@
##             main    #1713      +/-   ##
==========================================
+ Coverage   85.32%   85.33%   +0.01%     
==========================================
  Files        1269     1271       +2     
  Lines      114295   114511     +216     
  Branches    30195    30236      +41     
==========================================
+ Hits        97518    97715     +197     
- Misses      15729    15746      +17     
- Partials     1048     1050       +2     

Impacted Files	Coverage Δ
...ewModels/PledgePaymentMethodAddCellViewModel.swift	0.00% <0.00%> (ø)
...r-iOS/Views/Controllers/PledgeViewController.swift	72.93% <16.66%> (-0.73%)	⬇️
...ntrollers/PledgePaymentMethodsViewController.swift	46.47% <47.05%> (+1.86%)	⬆️
...ary/ViewModels/PledgePaymentMethodsViewModel.swift	96.64% <93.75%> (-0.18%)	⬇️
...S/DataSources/PledgePaymentMethodsDataSource.swift	88.88% <100.00%> (+2.35%)	⬆️
...aSources/PledgePaymentMethodsDataSourceTests.swift	99.17% <100.00%> (+0.05%)	⬆️
...r-iOS/Views/Cells/PledgePaymentMethodAddCell.swift	97.22% <100.00%> (+2.22%)	⬆️
...lers/PledgePaymentMethodsViewControllerTests.swift	100.00% <100.00%> (ø)
...iewModels/PledgePaymentMethodsViewModelTests.swift	97.90% <100.00%> (+0.11%)	⬆️
Library/Navigation.swift	85.20% <0.00%> (-0.65%)	⬇️
... and 1 more

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