feat(paywalls): wire web_view messaging into the paywall (PWENG-98)

[alexrepty]

Checklist

• If applicable, unit tests
• If applicable, create follow-up issues for purchases-ios and hybrids

Motivation

Exposes web_view bidirectional messaging to integrating apps and installs the bridge in the rendered paywall — the final piece that makes the feature usable end to end.

Resolves PWENG-98.

Description

• Adds the public PaywallOptions.setWebViewMessageHandler(...) opt-in, threaded through PaywallState / OfferingToStateMapper / PaywallViewModel.
• WebViewComponentView constructs and lifecycle-manages the bridge per rendered web_view (scoped by the component id), refreshing locale / handler across recompositions and tearing it down on release.
• Adds componentId to the web_view style/factory and regenerates ui/revenuecatui/api.txt for the new public handler API.
• Tested by PaywallOptionsWebViewHandlerTest.

iOS parity: mirrors purchases-ios (web-view-bridge-wiring) (onPaywallWebViewMessage there).
Stack (merge bottom-up): schema → rendering → CSP → value types → message model → variables provider → JS bridge → wiring.

---

Note

Medium Risk
Touches WebView JS bridging and a new public callback surface; mistakes could affect message delivery or WebView lifecycle, but purchase/dismiss are not auto-triggered by messages.

Overview
Adds PaywallOptions.setWebViewMessageHandler (public API + api.txt) so apps can observe Paywalls V2 web_view messages and reply via PaywallWebViewController. The handler is threaded through PaywallState.Loaded.Components, OfferingToStateMapper, and PaywallViewModel.

WebViewComponentView now creates a WebViewJavaScriptBridge per rendered web view when the style has a componentId (new field from WebViewComponent.id in StyleFactory), injects the shim on page start, refreshes locale/handler on recomposition, and releases on dispose. Handler-only updateOptions changes refresh in place (handler excluded from hashCode, like the listener) without rebuilding paywall state; workflow pre-warmed steps get the same stamp.

Tests cover builder/equality/hash behavior and view-model/workflow handler refresh.

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[alexrepty]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat(paywalls): wire web_view messaging into the paywall (PWENG-98) #3653 👈 (View in Graphite)
• feat(paywalls): add web_view JavaScript bridge (PWENG-98) #3655
• feat(paywalls): add web_view SDK variables provider (PWENG-98) #3663
• feat(paywalls): add web_view message model and parsing (PWENG-98) #3654
• feat(paywalls): add web_view message value types (PWENG-98) #3662
• feat(paywalls): isolate web_view content with a fixed CSP (PWENG-98) #3652
• feat(paywalls): render web_view component (PWENG-98) #3651
• feat(paywalls): add web_view component schema (PWENG-98) #3650
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.54%. Comparing base (28307d9) to head (ee282eb).

Additional details and impacted files

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  Lines                                   16606    16606           
  Branches                                 2373     2373           
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  Hits                                    13376    13376           
  Misses                                   2291     2291           
  Partials                                  939      939           

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