Validate user-supplied tree URIs in DocumentsProvider calls

Currently we only validate DocumentsContract.EXTRA_URI, this change
validates other URIs suchs as DocumentsContract.EXTRA_TARGET_URI and
DocumentsContract.EXTRA_PARENT_URI as well

Bug: 157320716
Test: Manually using the test app in b/157320716#comment1
Change-Id: I90fd1e62aa7dc333bf32eb80ccc5b181a1d54e41