DatePicker: fix handleClear #21301

[duowb]

datetimepick selects only one date. When it is cleared, clicking again is invalid #21301

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fix: #21301

or

     handleClear() {
        this.minDate = null;
        this.maxDate = null;
        this.rangeState.selecting = false;
        this.leftDate = calcDefaultValue(this.defaultValue)[0];
        this.rightDate = nextMonth(this.leftDate);
        this.$emit('pick', null);
      },

The code of month range may also have problems