chore(onefingerpan): update onefingerpan preference summary and magnification...

chore(onefingerpan): update onefingerpan preference summary and magnification settings page footer description

Based on b/338409557#comment5, we update the onefingerpan toggle's
summary, and make the magnification settings page's footer HTML
description be dynamic based on one finger panning preference state.

Bug: 338409557
Flag: com.android.server.accessibility.enable_magnification_one_finger_panning_gesture
Test: manually
      atest MagnificationOneFingerPanningPreferenceControllerTest
      atest ToggleScreenMagnificationPreferenceFragmentTest
      atest ToggleFeaturePreferenceFragmentTest
Change-Id: I817cad4fb0c034bcd2db0485ca27c30ea88a0280