Apply selected state to custom boost field instead of relying on focus.

app/src/main/java/org/thoughtcrime/securesms/components/settings/app/subscription/boost/Boost.kt

@@ -170,6 +170,7 @@ data class Boost(
         custom.setText("")
       }
 
+      custom.isSelected = model.isCustomAmountFocused
       custom.setOnFocusChangeListener { _, hasFocus ->
         model.onCustomAmountFocusChanged(hasFocus)
       }

app/src/main/res/drawable/rounded_outline_focusable_38dp.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <selector xmlns:android="http://schemas.android.com/apk/res/android">
-    <item android:drawable="@drawable/rounded_outline_accent_38dp" android:state_focused="true" />
+    <item android:drawable="@drawable/rounded_outline_accent_38dp" android:state_selected="true" />
     <item android:drawable="@drawable/rounded_outline_38dp" />
 </selector>