fix(slider): emit onchange callback correctly

Closes #7523

Author: Aleksandyr

projects/igniteui-angular/src/lib/slider/slider.component.ts

@@ -625,8 +625,6 @@ export class IgxSliderComponent implements
         } else {
             this._value = value;
         }
-
-        this._onChangeCallback(value);
     }
 
     /**
@@ -1420,13 +1418,24 @@ export class IgxSliderComponent implements
     public setValue(value: number | IRangeSliderValue) {
         if (!this.isRange) {
             this.upperValue = value as number - (value as number % this.step);
+            this._onChangeCallback(this.upperValue);
         } else {
             value = this.validateInitialValue(value as IRangeSliderValue);
             this.upperValue = (value as IRangeSliderValue).upper;
             this.lowerValue = (value as IRangeSliderValue).lower;
+            this._onChangeCallback({lower: this.lowerValue, upper: this.upperValue});
         }
+
+        // this.executeOnChange();
     }
 
+    // private executeOnChange() {
+    //     if (this.isRange) {
+    //     } else {
+
+    //     }
+    // }
+
     private emitValueChanged(oldValue: number | IRangeSliderValue) {
         this.onValueChange.emit({ oldValue, value: this.value });
     }