Integrate modifier keys settings UI with APIs

1. getModifierKeyRemapping
2. remapModifierKey
3. clearAllModifierKeyRemappings

Demo: go/modifier_keys_settings_demo

Bug: 244535460
Test: local test
Change-Id: I47bcd0b58637feb68c579112a991371490af0157
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index a794d8e..48b8eb2 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -127,6 +127,7 @@
     <uses-permission android:name="android.permission.START_VIEW_APP_FEATURES" />
     <uses-permission android:name="android.permission.LIST_ENABLED_CREDENTIAL_PROVIDERS" />
     <uses-permission android:name="android.permission.CUSTOMIZE_SYSTEM_UI" />
+    <uses-permission android:name="android.permission.REMAP_MODIFIER_KEYS" />
 
     <application
             android:name=".SettingsApplication"