[DocsUI, Search]: Put debug logs behind DEBUG flag.

Moves debug log statements introduced by Search V2 behind the if (DEBUG)
statements.

Bug: 423756845
Test: m DocumentsUIGoogle
Flag: com.android.documentsui.flags.use_search_v2_read_only
Change-Id: I4583970e92b2b45d1372ea7485a3d6c0ef60eaa8