Strip IME insets from browser WebView to prevent double padding

[lmac012]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1205617573940217/task/1217145253883158?focus=true
Tech Design URL (if applicable):
API Proposals URL(s) (if applicable):

Description

Since WebView M139, the WebView shrinks its visual viewport by any IME inset it receives. Our layout already resizes for the keyboard, so during IME entry both mechanisms briefly apply at once, transiently collapsing the visual viewport. This was confirmed to cause breakage on gemini.google.com, where collapsing the visual viewport clears composer focus and hides the on-screen keyboard, making it nearly impossible to use the site.

Fix: zero out ime() insets before they reach the browser WebView, as recommended in Google's WebView insets guidance.

Steps to test this PR

Keyboard stays open on Gemini

• Navigate to https://gemini.google.com in the browser
• Tap the message composer
• Verify the keyboard opens and stays open (before this fix it dismissed itself within ~100ms)
• Dismiss the keyboard and repeat the test a couple of times

Kill switch

• Disable androidBrowserConfig > stripWebViewImeInsets in internal feature flag settings
• Restart the app
• Navigate to https://gemini.google.com
• Tap the message composer
• Verify the keyboard dismisses itself almost immediately after being shown
• If the keyboard didn't dismiss itself (may happen occasionally), dismiss it and test again.

No UI changes

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Note

Medium Risk
Changes keyboard and viewport behavior for all in-app browsing when enabled; mitigated by a remote kill switch and a narrow inset adjustment.

Overview
Fixes keyboard dismissal and visual viewport collapse on sites like Gemini when WebView M139 shrinks the visual viewport for IME insets while the browser layout already resizes for the keyboard.

DuckDuckGoWebView now optionally zeros ime() insets in onApplyWindowInsets before they reach the WebView, following Android’s WebView inset guidance. BrowserTabFragment enables this via setStripImeInsetsEnabled after reading androidBrowserConfig.stripWebViewImeInsets (defaults on). Disabling the flag restores the old double-padding behavior for verification.

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