[DocsUI M3] Replace TextView to MaterialTextView

TextView will be inflated to MaterialTextView inside the Material theme,
so this change won't change any UI or functionality of he app, but as
our convention we always want to use the fully qualified component name,
we've done similar things on Button -> MaterialButton.

Bug: 406140464
Test: m DocumentsUIGoogle && manual inspection
Flag: com.android.documentsui.flags.use_material3
Change-Id: I7ff61dab8b32759c95115132a0c1f0fc6cda719d