QFontMetrics::width() is deprecated

[mmmaisel]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

There is a compiler warning about deprecation of QFontMetrics::width.

Expected Behavior

No warnings.

Steps To Reproduce

Compile from source.

Environment

- OS: Arch Linux (22. April 2022)
- AntiMicroX version: git 85bbc6bf

Anything else?

QFontMetrics::width() is deprecated since Qt 5.11 but the new function
QFontMetrics::horizontalAdvance() only exists since Qt 5.11.
This causes compilation errors on Ubuntu 18.4 and earlier if fixed.

[pktiuk]

Linked with: #318