[Development] Naming of path/directory-related environment variables in Qt

[Mitch Curtis]

I'd like to establish some kind of convention for naming path/directory-related environment variables in Qt, with the hope that it could be set in stone with e.g. one of these newfangled QUIPs.

Pelagicore (via Gordan) kindly contributed a patch to Qt Virtual Keyboard, where they introduced a QT_VIRTUALKEYBOARD_LAYOUTS_FOLDER environment variable:

https://codereview.qt-project.org/#/c/174616/

I then asked Gordan to change this to QT_VIRTUALKEYBOARD_LAYOUTS_DIR, as it seemed we had a few other environment variables using this naming scheme.

JP then pushed a patch that adds QT_QUICK_CONTROLS_STYLE_PATH to Qt Quick Controls 2:

https://codereview.qt-project.org/#/c/176512/

He found more examples of where we've used "PATH" than where we used "DIR", so it seems like a good time to continue with that trend so that we don't have any more inconsistencies.

My hope is that enough approvers see this email (or QUIP) and its conclusion (whatever it may be) and -1 patches that go against the convention.

So, can we all agree on using "PATH" when naming environment variables that refer to paths?