[DocsUI Peek] Metadata sheet toggle button

Add the top bar's "info" toggle button to control the metadata sheet
state.

Bug: 382163145
Flag: com.android.documentsui.flags.use_material3
Flag: com.android.documentsui.flags.use_peek_preview_ro
Test: PeekUiTest#testMetadataSheet
Change-Id: I122e1365cf35633b9948162e0d0f01fe67d16f82