SYNTH: Renamed capacity and size getters for better clarity

Lower caps versions were conflicting with lower caps local variables.
All previous usage of these getters were updated accordingly.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
RINGBUFFER: Now using the proper getter for size and capacity

This is done instead of direct member variable access.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
RINGBUFFER: Fixed previously existing data within the ringbuffer discarded

The previous existing data (e.g. when size_ > 0) were sometimes ignored
when resizing, resulting in too much data being pushed in the buffer.

This is now fixed by adding the current size_ to the expected amount
of data to be popped from the buffer.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>