LineageParts: Migrate to androidx

* Migrate from support library to androidx

* Various improvements and cleanup by @bgcngm

Change-Id: Ic2596fd93abf8570fb4ce2239e99d3d862cf47b7
diff --git a/proguard.flags b/proguard.flags
index 85e774a..fb42f1e 100644
--- a/proguard.flags
+++ b/proguard.flags
@@ -19,7 +19,7 @@
   *** onClick*(...);
 }
 
--keep public class * extends android.support.v7.preference.* {
+-keep public class * extends androidx.preference.* {
     public <init>(android.content.Context, android.util.AttributeSet);
 }