audioresample and other audio filters with history: Does not work properly with negative rates playback

Submitted by Sebastian Dröge @slomo

Link to original bug (#757043)

Description

+++ This bug was initially created as a clone of Bug 757033 +++

Currently they handle reverse playback the same way as forwards playback. This will lead to discontinuities for every single buffer, as the first sample of the first buffer is going to be followed by the last sample of the next buffer. Filters with history will however handle it as if the last sample of the first buffer is followed by the first sample of the next one.

To solve this I propose we add a function to libgstaudio to reverse all samples in a buffer, and then have these filters set applied_rate to -1.0 and rate to -rate.