Default height range modifiers to visible layer(s) in Preview

**Is your feature request related to a problem? Please describe.** The "Height range Modifier" (HRM) feature has no intuitive way to modify the active layer under inspection. That is, when dragging the top-handle of the visible layers range down from the top of the model. Similarly, using the bottom handle as well lets the user visually select a range of layers to target. While the HRM feature is based on heights within the model, I find myself targeting specific layer(s) instead. The feature (in terms of UI) feels bare-bones and does not integrate into the editor or the user's workflow. When creating an HRM it defaults to the first 0.2mm of the model; using the active state of the editor gives the user a more intuitive experience to modify their active selection(s). **Describe the solution you'd like** When the view is in Preview mode, a new HRM bases its defaults on the user's layers selection. Additionally, the "Settings for Height range" form has two buttons: 1) to set the range to the top-layer shown in preview, 2) to set the range to all shown layers in the preview. With (1) this lets the user easily update the range to a specific layer they are looking at. And with (2) a user can use both bottom and top handles in order to select multiple layers. **Describe how it would work** When a new HRM is created by the user, and the editor shows the Preview of a sliced model, then the HRM uses the visible layers to determine what range to default to. 1. If the editor is in preview, and the bottom handle is set to the base layer, the HRM is set to select the top-layer shown in the preview. 2. If the editor is in preview, and the bottom handle is not set to the base layer, the HRM is set to select the range of layers visible in the preview. Note: with (1), a user may actually want to target from the base layer upwards, so set the range in such a way that if the user changes the start height to 0, it would then exactly select that range that was visible at creation of the HRM. **Describe alternatives you've considered** Currently I have to look at a specific slice at height, then set the start to below that and end after that. Unfortunately as soon as I create or modify an HRM, the preview leaves because the slice settings changed. This is rather poor experience to try and find the right way to configure this. **Additional context** It would also be great if the 3d view would visually show a selected HRM's range on the rendered model, by using a different color or something.