Refactor how AppSearchResult and AppSearchBatchResult are parcelled.

Mainline modules seem to be metalava'd differently, causing the CREATOR,
describeContents(), and other parcelling methods to become part of the
public API.

Additionally, AppSearchResult and AppSearchBatchResult were forked from
Jetpack with parcelling added, and manually maintained.

Additionally, the parcelling wouldn't work properly if the keys and
values are not themselves parcelable, but this was not clearly
documented or called out.

This CL fixes these problems by creating parcelable wrappers around the
upstream Jetpack AppSearchResult and AppSearchBatchResult, usable only
when they contain parcelable keys and values.

Bug: 146218515
Test: Presubmit
Change-Id: I828a22dc6dae3e46f5d167f1a9d12627ba15d9fd