erasure-code: ErasureCode base class

Add the ErasureCode base class for ErasureCodeJerasure and
ErasureCodeIsa, for methods that can be shared among all plugins.

http://tracker.ceph.com/issues/8496 Fixes: #8496

Signed-off-by: Loic Dachary <loic@dachary.org>
erasure-code: move to ErasureCode::{encode,decode}{,chunk}

The bulk of ErasureCode{Jerasure,Isa}::encode and
ErasureCode{Jerasure,Isa}::decode is dealing with alignment and buffer
allocation. This is moved to ErasureCode::encode and ErasureCode::decode
respectively.

The jerasure/isa specific code is isolated in the new
ErasureCode{Jerasure,Isa}::encode_chunks and
ErasureCode{Jerasure,Isa}::decode_chunks virtual functions.

http://tracker.ceph.com/issues/8496 Refs: #8496

Signed-off-by: Loic Dachary <loic@dachary.org>
erasure-code: move to ErasureCode::minimum_to_decode*

The ErasureCode{Jerasure,Isa}::minimum_to_decode and
ErasureCode{Jerasure,Isa}::minimum_to_decode_with_cost methods are moved
verbatim to the ErasureCode base class.

http://tracker.ceph.com/issues/8496 Refs: #8496

Signed-off-by: Loic Dachary <loic@dachary.org>
erasure-code: move to ErasureCode::to_{int,bool}

The parameter parser helpers to_int and to_bool are moved from
ErasureCode{Jerasure,Isa} to ErasureCode.

The prototype is modified to return a status instead of the value. An
error ostream is provided as the last argument because ErasureCode
cannot use dout() or derr().

http://tracker.ceph.com/issues/8496 Refs: #8496

Signed-off-by: Loic Dachary <loic@dachary.org>
erasure-code: move to ErasureCode::decode_concat

It does not belong to ErasureCodeInterface which is supposed to not have
any implementation.

Signed-off-by: Loic Dachary <loic@dachary.org>
erasure-code: rework ErasureCode*::parse methods

The ErasureCode::parse virtual function is derived in
ErasureCode{Jerasure,Isa}. It is reworked to share parsing arguments the
various techniques have in common. The logic is otherwise unmodified.

http://tracker.ceph.com/issues/8496 Refs: #8496

Signed-off-by: Loic Dachary <loic@dachary.org>