Resolve "VARIABLE_SPEED_DECODING does not work"

• Related issues: #899 (closed)
• Requested reviewers:

Reason why this change is needed

Enabled switch VARIABLE_SPEED_DECODING. Tried to build, but building crashes. Seems to be related to 5 ms, since the error is:

error: no member named 'enable5ms' in 'DecArguments'

Description of the change

Fix build with enabled switch VARIABLE_SPEED_DECODING, generally fix the variable speed decoding to apply as much TSM as possible.

Affected operating points

• None
• Produced bitstream is BE compared to previous state (no encoder changes).

Related to #899 (closed)