[DocsUI, Search]: Adds more tests for exceptions

Adds a test similar to that in FolderLoaderTest, that validates
SearchLoader behavior in the presence of exceptions.

Bug: 427555916
Test: atest DocumentsUIGoogleTests
Flag: com.android.documentsui.flags.use_search_v2_read_only
Change-Id: Ifa183f4f3cdbbd02ea5427e18c06c91184200fda