Changing Android embedder keyboard logic to check if the key event originates from a software keyboard using Android's native KeyCharacterMap.VIRTUAL_KEYBOARD device identifier (deviceId == -1):

boolean isVirtualKeyboard = event.getDeviceId() == android.view.KeyCharacterMap.VIRTUAL_KEYBOARD;

When META_SHIFT_ON is active, the KeyEmbedderResponder will now trust the current state for virtual keyboards and skip synthesizing missing physical modifier keys.

Why this works:

1. Fixes Gboard Shift: When Gboard sends ShiftLeft UP but keeps META_SHIFT_ON active (to signify Shift lock), Flutter will no longer synthesize a phantom ShiftRight DOWN. The framework will correctly register that NO physical shift keys are held down, so tapping the screen will no longer trigger a shift-click text selection.
2. Fixes Backspace/Enter: If you type another virtual key (like Backspace) while META_SHIFT_ON is active, Flutter will no longer synthesize a phantom ShiftLeft DOWN.
3. Preserves Hardware Keyboard Fallbacks: ChromeOS and external physical keyboards (which do not use VIRTUAL_KEYBOARD as their device ID) will continue to have missing modifier keys correctly synthesized by Flutter if their hardware drops the DOWN events.

Fixes: #184744

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
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• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• I followed the [breaking change policy] and added [Data Driven Fixes] where supported.
• All existing and new tests are passing.