[PM-39564] feat: Fill Assist support email field key for email-based login forms

[aj-rosado]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-39564

📔 Objective

Fill-assist rules in the forms JSON use "email" as the field key for sites where users log in with their email address (e.g. { "email": ["input[type='email']"] }). Previously this key was unrecognised — it fell through to else -> null in toAutofillViewForFieldKey, so autofill never triggered for those fields.

This PR adds a dedicated AutofillView.Login.Email sealed subtype and wires it through the fill pipeline with a validation guard: the email field is only filled when the cipher's stored username contains @. If the username is not an email address the field is skipped, avoiding placing a non-email value into an type="email" input.

• AutofillView.Login.Email added alongside Username and Password
• Fill-assist "email" key maps to Login.Email in toAutofillViewForFieldKey
• FilledDataBuilderImpl guards Login.Email: skips fill when username does not pass isValidEmail(useStrictValidation = false)
• AutofillPartitionExtensions.usernameSaveValue updated to capture Login.Email text values so saving credentials from email-only forms preserves the typed value
• All exhaustive when expressions on AutofillView updated (AutofillViewExtensions, AutofillParserImpl.updateWebsiteIfNecessary)

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.05%. Comparing base (ec4ec39) to head (f90e3a0).

Files with missing lines	Patch %	Lines
...twarden/data/autofill/parser/AutofillParserImpl.kt	0.00%	0 Missing and 1 partial ⚠️
...arden/data/autofill/util/AutofillViewExtensions.kt	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                             Coverage Diff                              @@
##           PM-38966/add-fill-assist-option-settings    #7107      +/-   ##
============================================================================
- Coverage                                     86.06%   86.05%   -0.01%     
============================================================================
  Files                                           886      886              
  Lines                                         64627    64635       +8     
  Branches                                       9624     9629       +5     
============================================================================
+ Hits                                          55618    55624       +6     
- Misses                                         5560     5561       +1     
- Partials                                       3449     3450       +1     

Flag	Coverage Δ
app-data	17.67% <77.77%> (+0.01%)	⬆️
app-ui-auth-tools	18.76% <0.00%> (-0.01%)	⬇️
app-ui-platform	16.51% <0.00%> (-0.01%)	⬇️
app-ui-vault	27.43% <0.00%> (-0.01%)	⬇️
authenticator	6.12% <0.00%> (+<0.01%)	⬆️
lib-core-network-bridge	4.04% <0.00%> (-0.01%)	⬇️
lib-data-ui	1.13% <0.00%> (-0.01%)	⬇️

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