VSE: Add sound strip retiming support

This patch contains changes needed for retiming sound strips. This is a part of blender/blender#104544

----

Deviation from blender/blender#100337 is, that changes in audaspace are not separated.
Versioning for old files is not present, because resulting data is unusable (whole animation is baked, so changing retiming is basically impossible). Versioning also results in precision issues which results in non uniform sound pitch in some cases. And finally calculating strip offset correction is non-trivial (that is least of an issue, but worth mentioning still). So I would advocate to not convert old data to current implementation. I think, that supporting smooth speed transitions would allow for more efficient versioning code.

@@ -167,1 +167,4 @@
 
+AUD_API void AUD_SequenceEntry_setAnimationData_constant_range(AUD_SequenceEntry* entry, AUD_AnimateablePropertyType type, int frame_start, int frame_end, float* data)
+{
+  AnimateableProperty* prop = (*entry)->getAnimProperty(static_cast<AnimateablePropertyType>(type));

@@ -115,0 +118,4 @@
+   * \param position_start The start position in the animation in frames.
+   * \param position_end The end position in the animation in frames.
+   */
+  void write_range(const float* data, int position_start, int position_end);

@@ -64,2 +64,4 @@
 	double m_skip;
 
+  /// The FPS of the scene.
+  float m_fps;

@@ -245,3 +244,1 @@
-	if(seekpos < 0)
-		seekpos = 0;
-	seekpos += m_entry->m_skip;
+	float seek_frame = (position - m_entry->m_begin) * m_entry->m_fps;

@@ -248,0 +246,4 @@
+		seek_frame = 0;
+	seek_frame += m_entry->m_skip * m_entry->m_fps;
+
+	AnimateableProperty* pitch_property = m_entry->getAnimProperty(AP_PITCH);

@@ -248,0 +251,4 @@
+	float target_frame = 0;
+	if(pitch_property != nullptr)
+	{
+		for(int i = 0; i < seek_frame; i++)

@@ -71,0 +72,4 @@
+ * \param frame_end End of the frame range.
+ * \param data The data to write.
+ */
+AUD_API void AUD_SequenceEntry_setAnimationData_constant_range(AUD_SequenceEntry* entry, AUD_AnimateablePropertyType type, int frame_start, int frame_end, float* data);

@@ -115,0 +118,4 @@
+	 * \param position_start The start position in the animation in frames.
+	 * \param position_end The end position in the animation in frames.
+	 */
+	void write_constant_range(const float* data, int position_start, int position_end);

@@ -248,0 +283,4 @@
+
+class RetimingRangeData {
+ public:
+  std::vector<RetimingRange> ranges;

@@ -248,0 +303,4 @@
+
+  RetimingRangeData &operator*=(const RetimingRangeData rhs)
+  {
+    if (ranges.size() == 0) {