1. Apply attr/colorAccent to button icons for theme UI control
2. Apply attr/selectableItemBackground for button tapping ripple effect
3. Use ConstraintLayout to separate ssid EditText and scan button
4. Remove ButtonPreference and add AddNetworkPreference.
ButtonPreference's naming and design look like a general purpose UI
component but it's not. This change refactors the code.
5. In AddNetworkPreference, use settingslib layout file
'preference_access_point' to fix UI alignment problems.
Bug: 126964552
Bug: 125434239
Bug: 126762937
Test: manual test
atest com.android.settings.wifi.WifiSettingsTest
Change-Id: Ib899a1e10f96bb8427ff00d6b5dfca37a0642c44
