AdapterIO: add FlushBefore() to strip the beginning of the MallocIO object

by default, AdapterIO is initialized with a BMallocIO object, which will
be extended indefinitely. Flushing regularly is necessary to avoid
excessive memory usage. Tested in StreamRadio.

Change-Id: I9f3142c0a2300ad44dc54ccf6932d41c9526320b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7302
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

AdapterIO: only for SEEK_SET is the position absolute

Change-Id: I8debbcc0a2d9e499bebcebe5361475737dc8f9f0
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7295
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

Revert the Codec Kit.

All of Barrett's individual reverts have been squashed into this
one commit, save a few actual bugfixes.

Change-Id: Ib0a7d0a841d3ac40b1fca7372c58b7f9229bd1f0

media: Remove debug.h, finalize MediaDebug.h

* Funny rust from 0 AD.

AdapterIO: Fix -Wtautological compare.

* B_MEDIA_SEEKABLE was once a flag with one bit set. Due
to the complexity of streaming mediums, I had to split
this flag into B_MEDIA_SEEK_BACKWARD and B_MEDIA_SEEK_FORWARD
and never noticed that this broke the flag check.

* Reported by Murai Takashi through gcc8.

Populate media/experimental with future media_kit classes

* Node implementations headers are move into src/kits/media.