[DocsUI M3] Re-layout file list on window size change

Previously only a directory load or an app bar layout change
would re-layout the file list. A lot of small, incremental
window size changes would not trigger a re-layout leading to
a strange UI or overcrowded items or excessive space.

Update the layout whenever the AnimationView (the directory
fragment) observes a size change. Introduce an OnSizeChangedListener
to trigger the re-layout.

Also use the dimens grid_width, grid_height and grid_item_margin
on the grid item (item_doc_grid.xml) as these are also used by the
DirectoryFragment.java to get the correct spacing for the layout.

See bug for demo video.

Bug: 404625076
Test: m DocumentsUIGoogle && manual inspection
Flag: com.android.documentsui.flags.use_material3
Change-Id: I5e2a94757b8effc2462f818bc2fa286fefcd4740