Materials: Change display of Quantity values

The default display type of quantity objects is fixed point resulting
in insufficient accuracy when changing unit systems, or when the values
are small. This fix changes the default format from 'Fixed' to the more
apt 'Default' format. This allows the displayed values to scale as
appropriate.

Fixes #18149

tests/src/Mod/Material/App/TestMaterials.cpp

@@ -37,6 +37,7 @@
 #include <src/App/InitApplication.h>
 
 #include <Mod/Material/App/MaterialManager.h>
+#include <Mod/Material/App/MaterialValue.h>
 #include <Mod/Material/App/Model.h>
 #include <Mod/Material/App/ModelManager.h>
 #include <Mod/Material/App/ModelUuids.h>
@@ -223,7 +224,9 @@ TEST_F(TestMaterial, TestAddAppearanceModel)
 QString parseQuantity(const char *string)
 {
     QString value = QString::fromStdString(string);
-    return Base::Quantity::parse(value).getUserString();
+    auto quantity = Base::Quantity::parse(value);
+    quantity.setFormat(Materials::MaterialValue::getQuantityFormat());
+    return quantity.getUserString();
 }
 
 TEST_F(TestMaterial, TestCalculiXSteel)