Set conversation icon x at shelf start when fading into shelf

Conversation avatar show icons as right badge in LTR, left badge
in RTL. If we use x translation as is, the icon will fade into
the shelf in the middle instead of at the start.

This change fades in conversation icons at shelf start.

Bug: 178479515
Test: conversation icons fade into shelf at shelf start in LTR/RTL
Change-Id: I99ada3915e49160609839ae5562bccc7327f8c7b