Enlarge pointer icon for magnification

When full screen magnification is enabled, pointer icons should be also
enlarged by the zoom factor.

This change adds an API in InputManagerInternal for accessibility to
update the scale factor when full screen magnification is enabled.

Currently there's only one caller, but it will be called from more
places in future changes.

Bug: 355734856
Test: Enable flag, and changing scale with slider or gesture will change pointer icons.
Test: PointerIconCacheTest
Test: atest com.android.server.accessibility.magnification
Flag: com.android.server.accessibility.magnification_enlarge_pointer

Change-Id: I985183b12d6a1c4a6aa4c53e4f462778aeb2e9ae