Resolve "5ms and 20ms rendering not BE for OSBA and STEREO"

• Related issues: #979 (closed)
• Requested reviewers: @weckbecker, @tyagiri

Reason why this change is needed

Decoding with 5ms and 20ms is not BE for most OSBA outputs (mono and binaural are fine, the rest is not BE), same for STEREO to non-stereo output configurations.

Description of the change

Set offsets into the common buffers for transport channels access correctly for OSBA and STEREO. Fix a small inconsitency between the number of TC init and the number of common buffer channels init for BINUARAL/STEREO output and OMASA.

Affected operating points

• BE for 20ms, non-BE for 5ms and OSBA with discrete objects.
• Produced bitstream is BE compared to previous state (no encoder change).

Related to #979 (closed)