a11y: Initialize slider position with cursor area size setting

When the preference loads, initialize the slider position using the
cursor area size value from settings.

In addition, match slider seekbar range and the cursor area size range.

Change-Id: Ib6a8ca8463358a3e2de5ae6be8afd5113a5826be
Bug: b/383901288
Test: ToggleAutoclickCursorAreaSizeControllerTest
Flag: com.android.server.accessibility.enable_autoclick_indicator