Send search result limit to DocumentProvider when supported

Certain DocumentsProviders (eg. DownloadStorageProvider and
ExternalStorageProvider) now advertise on their Roots that they allow a
max result limit to be specified rather than choosing it themselves.

When this is advertised, specify the limit so that potentially matching
search results are not artificially left out by the DocumentsProvider.

Flag: com.android.documentsui.flags.use_search_v2_read_only
Bug: 414495650
Test: atest 'DocumentsUIGoogleTests:com.android.documentsui.loaders.SearchLoaderTest'
Change-Id: I00a52c365c879780a4a71ae18e1479c027190c3c