fix(datetime): reset falls back to value if set

core/src/components.d.ts

@@ -819,7 +819,7 @@ export namespace Components {
     }
     interface IonDatetime {
         /**
-          * Emits the ionCancel event and optionally closes the popover or modal that the datetime was presented in.
+          * The cancel method performs the following actions: 1. Emits the ionCancel event 2. Resets the internal state of the datetime 3. Closes the parent popover or modal if "closeOverlay" is true.
          */
         "cancel": (closeOverlay?: boolean) => Promise<void>;
         /**

core/src/components/datetime/datetime.tsx

@@ -546,7 +546,7 @@ export class Datetime implements ComponentInterface {
    */
   @Method()
   async reset(startDate?: string) {
-    this.processValue(startDate);
+    this.processValue(startDate ?? this.value);
   }
 
   /**