[url_launcher_android] Fix WebView content obscured by navigation bar on Android 15+

[Ann3388p]

Fixes flutter/flutter#170333

Problem

On Android 15+ devices with button navigation bar, WebView content
launched via LaunchMode.inAppWebView is obscured by the system
navigation bar. Interactive elements like cookie banners are not tappable.

Fix

Added ViewCompat.setOnApplyWindowInsetsListener to WebViewActivity
to apply proper padding based on system window insets, ensuring WebView
content respects the navigation bar area.

Testing

Tested on Android 15 emulator with button navigation enabled.

"Note: The existing unit tests fail to compile due to a pre-existing Robolectric 4.16 compatibility issue unrelated to this change. This can be verified by running tests on the unmodified main branch."

Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.

List which issues are fixed by this PR. You must list at least one issue.

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
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• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
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• I linked to at least one issue that this PR fixes in the description above.
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• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
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[gemini-code-assist]

Code Review

This pull request updates the url_launcher_android package to version 6.3.31, implementing a WindowInsetsListener in WebViewActivity to prevent content from being obscured by the system navigation bar on Android 15+. It also adds a Robolectric unit test to verify WebView initialization. Review feedback identifies several Java style guide violations, including out-of-order imports, inconsistent 2-space indentation in both source and test files, and a missing trailing newline.

[gemini-code-assist]

These imports are out of order. According to the Google Java Style Guide, imports should be grouped by package and sorted alphabetically. These androidx imports should be placed with the other androidx imports (around line 23).

References

1. Code should follow the relevant style guides for each language (Google Java Style for Java). ^(link)

[gemini-code-assist]

The indentation of this block is incorrect and does not match the 2-space indentation used in the rest of the file. The closing brace is also misaligned.

    ViewCompat.setOnApplyWindowInsetsListener(
        webview,
        (v, insets) -> {
          Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
          v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
          return insets;
        });

References

1. Code should follow the relevant style guides for each language (Google Java Style for Java). ^(link)

[gemini-code-assist]

The indentation of the Robolectric.buildActivity call is inconsistent with the 2-space indentation used in the project.

    WebViewActivity activity =
        Robolectric.buildActivity(
            WebViewActivity.class,
            WebViewActivity.createIntent(
                ApplicationProvider.getApplicationContext(),
                "https://flutter.dev",
                false,
                false,
                new Bundle()))
            .create()
            .get();

References

1. Code should follow the relevant style guides for each language (Google Java Style for Java). ^(link)

[gemini-code-assist]

The file is missing a newline character at the end.

Suggested change

	}
	}

References

1. Code should follow the relevant style guides for each language (Google Java Style for Java). ^(link)