watt-toolkit: Add version 2.8.4

[bobo2334]

Watt Toolkit (former name Steam++) is an open source cross-platform multi-purpose game toolkit, most of its features require you to download and install Steam to use it.

• [x] I have read the Contributing Guide.

[bobo2334]

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[github-actions[bot]]

All changes look good.

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watt-toolkit

• [x] Description
• [x] License
• [x] Hashes
• [x] Checkver
• [x] Autoupdate
• [x] Autoupdate Hash Extraction

[H-Tung]

The latest version of the software is 2.8.6, thus the download URL and hash info need to be updated accordingly.