Enable resource shrinking of APK DocumentsUI

This change enable R8 resources shrinking for DocumentsUI.

The size of DocumentUI will be reduced by 9% from 6864931B to 6206354B.

The removed resources symbols can be found
https://drive.google.com/file/d/1xOF6Px5AEaN_scCCOYmiDOTBmmcPqvsm/view?usp=sharing.

The removed resource files can be found
https://drive.google.com/file/d/1lFqf6Ky_NHZphzeNvPoIqUinwwmxhqo0/view?usp=sharing

Test: presubmit
Bug: 259106853
Change-Id: Ieab84d3a107c3a80f896d532d6984510c561f666