Utilize promises in triggerMouseEvent and fixture.run

[kurkle]

With async triggerMouseEvent, the tests can be a lot cleaner, for example:

https://github.com/chartjs/Chart.js/blob/4491732ad59b7796ba04cae878fa804717e91c2f/test/specs/controller.bubble.tests.js#L293-L314

		it ('should handle default hover styles', function(done) {
			var chart = this.chart;
			var point = chart.getDatasetMeta(0).data[0];

			afterEvent(chart, 'mousemove', function() {
				expect(point.options.backgroundColor).toBe('#3187DD');
				expect(point.options.borderColor).toBe('#175A9D');
				expect(point.options.borderWidth).toBe(1);
				expect(point.options.radius).toBe(20 + 4);

				afterEvent(chart, 'mouseout', function() {
					expect(point.options.backgroundColor).toBe('rgb(100, 150, 200)');
					expect(point.options.borderColor).toBe('rgb(50, 100, 150)');
					expect(point.options.borderWidth).toBe(2);
					expect(point.options.radius).toBe(20);

					done();
				});
				jasmine.triggerMouseEvent(chart, 'mouseout', point);
			});
			jasmine.triggerMouseEvent(chart, 'mousemove', point);
		});

Can be written like:

		it ('should handle default hover styles', function(done) {
			var chart = this.chart;
			var point = chart.getDatasetMeta(0).data[0];

			await jasmine.triggerMouseEvent(chart, 'mousemove', point);
			expect(point.options.backgroundColor).toBe('#3187DD');
			expect(point.options.borderColor).toBe('#175A9D');
			expect(point.options.borderWidth).toBe(1);
			expect(point.options.radius).toBe(20 + 4);

			await jasmine.triggerMouseEvent(chart, 'mouseout', point);
			expect(point.options.backgroundColor).toBe('rgb(100, 150, 200)');
			expect(point.options.borderColor).toBe('rgb(50, 100, 150)');
			expect(point.options.borderWidth).toBe(2);
			expect(point.options.radius).toBe(20);
		});

And a fixture run script like:

    run: (chart, done) => {
      var elem = chart.getDatasetMeta(0).data[0];
      afterEvent(chart, 'mousemove', () => {
        done();
      });
      triggerMouseEvent(chart, 'mousemove', elem.tooltipPosition());
    }

Would become

  run: (chart) => {
    var elem = chart.getDatasetMeta(0).data[0];
    return triggerMouseEvent(chart, 'mousemove', elem.tooltipPosition());
  }