Respond to API feedback on DIRECTORY columns.

Internal feedback asked for more documentation, and feedback from
external teams (at least Photos and Camera) was the ability to store
files at arbitrary directory depths.

We now offer a single PATH column, which gives callers more precise
control over file placement.  The old DIRECTORY columns remain
intact for now, and are temporarily accepted to support apps
developing against the preview SDKs.

Bug: 127657692, 123967243
Test: atest MediaProviderTests
Test: atest cts/tests/tests/provider/src/android/provider/cts/MediaStore*
Change-Id: Icd90d7c89d066d4ab68aa2f543ccc6fbc3b4f596