Fix native text input SendInput layout

[enaboapps]

Summary

• fix the Win32 INPUT union layout used by the native text input helper on x64
• reserve the full native union size so SendInput accepts Unicode keyboard input records

Closes #212

Proof

Created isolated proof harness at C:\Users\oamcg\source\repos\switchify-text-input-proof.
It opens a real WinForms TextBox, focuses it, sends Unicode text with SendInput(KEYEVENTF_UNICODE) only, then reads the textbox value back.

Result:

sentEvents=60
expectedLength=31
actualLength=31
match=True

No clipboard fallback was used.

Verification

• dotnet run -c Release in C:\Users\oamcg\source\repos\switchify-text-input-proof
• npm run native:build
• npm run native:smoke-text
• npm test
• npm run build