Allow custom properties to be assigned a unique color to show inside of tileview/mapview/tileset preview windows

[jonatino]

Is your feature request related to a problem? Please describe.
I love how flexible Tiled is with custom properties. It allows me to keep all my map related configs in one editor. My biggest gripe with tiled is it's impossible to visually see what tiles have custom properties and which dont.

Describe the solution you'd like
It'd be amazing if we could assign a color value to each property type (optional maybe?) and use that color to outline the tile on the mapview/tileview/tileset preview window. Also, show the color when the tile is selected next to the custom property itself.

Describe alternatives you've considered
Can't think of any other than using a different map editor. For example, I have an "interactable" property which allows me to configure if the tile is interactable in game or not. Currently, it's impossible to quickly see all the interactable tiles in your tileset.

It doesn't need to be a color either, just some sort of visual representation to see. I picked color since it would be easy to have several colors representing several properties by using a dashed outline with different colors.

[bjorn]

While I could imagine supporting such feature built-in, I will also refer to #2134, which is about allowing scripts to customize the appearance of objects. That issue does however not cover custom appearance of properties in the properties view, tiles in the tileset view and not even tiles in the map view (since it's only about objects).

[jonatino]

@bjorn support via script to customize a tiles visual appearance (wherever it is shown) would be great.