Fix ElementNode update/recycling

This CL fixes a subtle bug in the element update that would happen when
an ElementNode is updated with an Element that is different than the
previous one but with the same key, which can happen when the node is
recycled inside a lazy layout.

Bug: 308961608
Test: ElementTest
Flag: N/A
Change-Id: Iba8601627b23ebbd33cadb8ac2f1c619c403a1f8