Fix/android legacy viewport calculation

[ish1416]

Description

Fixes incorrect window.innerHeight and visualViewport.height values on Android < 15 devices, which cause UI elements to be partially overlapped by the keyboard when navigation bars are present.

Closes #8181

Problem

On Android < 15 devices with navigation bars (gesture or button navigation), the browser's viewport calculations don't account for the navigation bar height when the keyboard is open. This causes:

• Modals and dialogs to be positioned too low
• Bottom UI elements hidden behind keyboard
• safe-area-inset-bottom always returns 0
• Inconsistent behavior compared to Android 15+

Solution

Enhanced CapacitorWebView with native viewport correction:

1. Navigation bar height detection using Android system resources
2. Viewport override for visualViewport.height on Android < 15
3. CSS custom properties injection for --safe-area-inset-bottom
4. Automatic resize events to notify components

Testing

• ✅ OnePlus 12R (Android 14) - UI no longer overlapped
• ✅ Samsung S23 (Android 13) - Correct viewport calculations
• ✅ Pixel 8 (Android 14) - Bottom padding applied correctly
• ✅ No regression on Android 15+ devices

Breaking Changes

None - maintains full backward compatibility.