feature request: fast scroll

[ilf]

app: org.lineageos.eleven
name: Eleven
version: 4.2.0

With lots of audio files, Eleven gets really hard to navigate and find things.
In addition to search (#17), fast scroll would be awesome.

https://developer.android.com/reference/android/widget/AbsListView.html#attr_android:fastScrollEnabled
https://developer.android.com/reference/android/widget/AbsListView.html#setFastScrollEnabled(boolean)

com.android.contacts uses this, apparently like this:

$ grep -Ri fastscroll
src/com/android/contacts/list/ContactEntryListFragment.java:            mListView.setFastScrollEnabled(hasScrollbar);
src/com/android/contacts/list/ContactEntryListFragment.java:                mListView.setFastScrollEnabled(!flag);
src/com/android/contacts/list/ContactEntryListFragment.java:        mListView.setFastScrollEnabled(!isSearchMode());
res/layout/contact_list_content.xml:                android:fastScrollEnabled="true"
res/layout/join_contact_picker_list_content.xml:            android:fastScrollEnabled="true"
res/layout/contact_picker_content.xml:        android:fastScrollEnabled="true"/>