Provide a way to Magnification settings via intent

Framework needs a way to launch magnification settings.

bug: 168635084
Test: adb shell am start -a \
     "android.settings.ACCESSIBILITY_DETAILS_SETTINGS"  \
     --es android.intent.extra.COMPONENT_NAME  \
     "com.android.server.accessibility/Magnification"
     AccessibilityDetailsSettingsFragmentTest
Change-Id: Iafb5ad4802a52e4bf3c443af99cd27ef0da0ea29