[ios] Evaluate performance of removing/adding constraints in updateScaleBar

[julianrex]

Follow-on to PR #13911

Since the intrinsic content size of the scale may change frequently during a camera "fly to", we should revisit whether it's necessary to call -installScaleBarConstraints in updateScaleBar:

Since the scale bar constraints are set up with constants:

[updatedConstraints addObject:[view.widthAnchor constraintEqualToConstant:size.width]];
[updatedConstraints addObject:[view.heightAnchor constraintEqualToConstant:size.height]];

it shouldn't be necessary to remove and re-add the height and width constraints: instead it should be more performant to update the constraints' constant.

We should:

• Evaluate the performance impact of the original change.
• Compare with updating the constant value only.

/cc @lloydsheng @friedbunny

[lloydsheng]

@julianrex I had a benchmark for the changes on an iPhone 7 device, It seems to have no impact on performance.

	Before	After
Commit	5ccc5b7	60ceac5
Performance

The benchmark code as below:

- (void)updateCenterCoordinate {
    CLLocationCoordinate2D coordinate = self.mapView.centerCoordinate.latitude <= 31 ? CLLocationCoordinate2DMake(60, 0) : CLLocationCoordinate2DMake(30, 180);
    __weak MBXOrnamentsViewController *wself = self;
    [self.mapView setCenterCoordinate:coordinate zoomLevel:16 direction:30 animated:true completionHandler:^{
        [wself updateCenterCoordinate];
    }];
}

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