Currently, DPIUtil#isMonitorSpecificScalingActive() returns true if the
according system property has an appropriate value. However,
monitor-specific scaling will effectively never be active when using
Linux or MacOS, as it is only implemented for Windows. Returning "true"
on a non-supported platform is inconsistent and puts the burden to take
into account if the OS is supported at all to the consumers.
This change thus adapts the method to always return "false" on
non-supported platforms. This also conforms to the documentation of the
system property in the DPIUtil class.