feat: add injectable stack nav, re-add theming

[bryce-mcmath]

Summary of Changes

This PR allows Bifold wallets to extend the RootStack with an optional custom stack navigator slot. It also reverts a recent change that remove theming from the PINInput.

Related Issues

N/A

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[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[bryce-mcmath]

@FarjadGov14 we had to add back the PINInputTheme.cell usage, as it broke the appearance in BC Wallet. You can edit this property in your theme.ts file to make it look however you like, but the theming should still be used so that Bifold users can customize it.