Add debug system property to guard Game Default Frame Rate

This patch adds a debug system property to disable Game Default
Frame Rate in run time.

Without setting UI implementation, toggleGameDefaultFrameRate() will
not be called to enable/disable Game Default Frame Rate. Here we guard
getGameDefaultFrameRate() to determine the frame rate value and further
diable this feature.

Bug: 286084594
Test: atest GameManagerServiceTests
Change-Id: I7744d8ac581ba1e1dc874143cad4d29ff97b35ec