DocumentsProvider: add video metadata support

MetadataReader: support mimetypes a la ExifInterface

DocumentsProvider: support reading exif metadata

MetadataReader is ported from AOSP android-12.0.0_r3,
frameworks/base/core/java/android/provider.

DocumentsProvider: fill mime-type on special files

prevents DocumentsUI from displaying a "null" and no icon

DocumentsProvider: use cursor extras for error when allowed

instead of toast + exception, use cursor extras for error string, as
reference recommends. DocumentsUI handles it and displays to user.

DocumentsProvider: detect symlink to dirs

tree: remove ceph.patch

this is unused since pacific rebase, which source is hosted in a new
standalone repo

DocumentsProvider: unify metadata row building

this also fix a case where full path are taken as display names

DocumentsProvider: simplify logging and toasting

Revert "CephMount: add missing IOException throw to mount()"

This reverts commit 3cc32c4928758dbbd559ddf85d419bda28721b4a.

Unneeded modification after 7eb7507da84e9c9405f4b8149e61378594c205aa

DocumentsProvider: wrap remaining mount() to throw IOE

CephFSDocumentsProvider: simplify mount setup handling

CephFSDocumentsProvider: improve log messages

add editorconfig

CephFSDocumentsProvider: root: improve naming

make title shorter, and move cephfs string to summary, which makes it
friendlier to stock DocumentsUI with phone screen

jni: update prebuilts from ceph v16.2.7 rebase, un-lfs

newer ndk r23.b toolchain seems to produce a lot smaller binaries, and
we can now get rid of lfs. old binraries are branched at
old-prebuilts-lfs branch on github.

build: require sdk runtime minimum 24

this restriction actually already exists for a long time, from libceph*
libraries. ceph needs:

ns_* from arpa/nameser.h, __INTRODUCED_IN_64(22)
{get,free}ifaddrs from ifaddrs.h,  __INTRODUCED_IN(24)

CephFSDocumentsProvider: lookup mime-type on symlinks

build: use maven central instead of jcenter

make mount timeout configurable