Reduce unnecessary context creation for display

Previously, getMinimalTaskSizeDp can be called twice for a display
rotation change, which may add 2~4ms latency.

Since per-display Resources is available, it can use directly
without creation. Also move the invocation to onConfigurationChanged
because display info change doesn't mean it will affect the result
of a resource.

Bug: 253610885
Test: DisplayContentTests#testSetForcedDensity

Change-Id: Iefc3af1eae55c6c4b8951124f104b81f5be3867f