Visualize the pressure as the opacity of ovals

Added a new feature to the touchpad visualizer where the pressure applied by each finger is represented by the opacity of the corresponding oval. The oval with the maximum pressure is fully opaque, while the opacity of the others is scaled relative to their pressure compared to the maximum.

Test: Build
Test: Manual Test
Bug: 366416734
Flag: com.android.hardware.input.touchpad_visualizer
Change-Id: I8e3c328378951f3498bd7323d147d6f38cdf85ac