set loading(loading) {
        if (this._loading !== loading) {
            this._loading = loading;
            if (!this.loader && loading) {
                this.loader = this.ce('div', {
                    class: 'loader-wrapper',
                });
                const spinner = this.ce('div', {
                    class: 'loader text-center',
                });
                this.loader.appendChild(spinner);
            }
            /* eslint-disable max-depth */
            if (this.loader) {
                try {
                    if (loading) {
                        this.prependTo(this.loader, this.wrapper);
                    } else {
                        this.removeChildFrom(this.loader, this.wrapper);
                    }
                } catch (err) {
                    // ingore
                }
            }
            /* eslint-enable max-depth */
        }
    }
Set the loading state for this form, and also show the loader spinner.
@param {boolean} loading - If this form should be 'loading' or not.