Utils: Make FilePathAspect::setDefaultValue take a QString

This sets the unexpanded value, so going to a "cooked" FilePath can
at least theoretically break. On the user side it saves a
roundtrip in a few cases, but is more ugly when the input is already
a proper FilePath.

Change-Id: I8a7e8f6d46fcc34c96b55e41d656dca933fbef4e
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/plugins/haskell/haskellsettings.cpp

@@ -33,8 +33,8 @@ HaskellSettings::HaskellSettings()
     // stack from brew or the installer script from https://docs.haskellstack.org
     // install to /usr/local/bin.
     stackPath.setDefaultValue(HostOsInfo::isAnyUnixHost()
-        ? FilePath::fromString("/usr/local/bin/stack")
-        : FilePath::fromString("stack"));
+        ? QLatin1String("/usr/local/bin/stack")
+        : QLatin1String("stack"));
 
     setLayouter([this] {
         using namespace Layouting;