qt: All tray menu actions call showNormalIfMinimized

Summary:
Completes backport of core PR14123 (commit 0a656f8):
https://github.com/bitcoin/bitcoin/pull/14123/commits/0a656f85a9c694f25b06c6464d6e986816eecd58

Depends on D4483.

Test Plan:
Build and run on OSX and Linux.
Minimize the window, and trigger any contextual event from dock icon
that requires the GUI to pop up, and check it works as expected.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D4484