[Settings] add @Readable back for block_untrusted_touches, maximum_obscuring_opacity_for_touch

These settings are marked @hide to encourage the usage of wrapper APIs.
They should still be readable for any app via the public APIs in
InputManager.

BUG: 183067125
Test: atest android.server.wm.WindowUntrustedTouchTest
Change-Id: I2a3aff0e3bb2ecfba439323fc09b353bd0f2106f

core/java/android/provider/Settings.java

@@ -15835,6 +15835,7 @@ public final class Settings {
          *
          * @hide
          */
+        @Readable
         public static final String BLOCK_UNTRUSTED_TOUCHES_MODE = "block_untrusted_touches";
 
         /**
@@ -15860,6 +15861,7 @@ public final class Settings {
          *
          * @hide
          */
+        @Readable
         public static final String MAXIMUM_OBSCURING_OPACITY_FOR_TOUCH =
                 "maximum_obscuring_opacity_for_touch";