Asset Browser: Add slider UI to pose blending

Add the Slider UI to pose blending. This adds a slider with percentages,
and controls for precision control and incremental control.

Reviewed By: sybren

Maniphest Tasks: T90182

Differential Revision: https://developer.blender.org/D14984

source/blender/editors/util/ed_draw.c

@@ -484,6 +484,7 @@ float ED_slider_factor_get(struct tSlider *slider)
 
 void ED_slider_factor_set(struct tSlider *slider, const float factor)
 {
+  slider->raw_factor = factor;
   slider->factor = factor;
   if (!slider->overshoot) {
     slider->factor = clamp_f(slider->factor, 0, 1);