Merge #12999: qt: Show the Window when double clicking the taskbar icon

Summary:
67bf2aa qt:Show the entire Window when double clicking on taskbar (Chun Kuan Lee)

Pull request description:

fix #12838

Tree-SHA512: 4498bc1fe52efeed3768d6bdd7941e4b036d52ae80d9c1b6679c6daa3a62aeda4cff0c91fe1c65afaea6049c59cb0296fdcbff63ecb342d518615a92361fda7f

Backport Core PR12999
https://github.com/bitcoin/bitcoin/pull/12999/files

Test Plan:

make check
# No good way to test this since I don't have a Windows dev machine.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D3203