Update App.js

[IniyalPalanisamy]

Removed the unused copyEmoji ref. Added input value validation in the searchEmoji function. Used some method to filter the emoji list based on the input value. Removed the title argument from the copyToClipboard function. Used a state variable copiedEmoji to keep track of the copied emoji and reset it after a certain time.

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• [ ] I've been assigned an issue related to this PR.
• [ ] I've used beautifiers.
• [ ] I've added my Project's name and description to Index.md
• [ ] I've made a README.md file for my Project.
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