Map pointer speed slider on mouse page to control mouse speed

Currently, the pointer slider on the mouse settings page is actually
controlling touchpad pointer speed. Modify this to instead control the
mouse pointer speed.

Bug: 398034722
Test: Manually on device
Flag: com.android.settings.keyboard.keyboard_and_touchpad_a11y_new_page_enabled
Change-Id: I66cec4ef0a758e250bab89c194073eb408402431