Import tileset as .tsx - not only create tileset as now

[ManPython]

Is your feature request related to a problem? Please describe.
Right now user have create tileset and then save as .tsx.
Looks that this is basic problem is in case is no option to import .tsx but create new and save/override exit this same if user want use this same tile set.

Describe the solution you'd like
Import like Export.

Describe alternatives you've considered
Right now trying copy path to .tsx in to .tmx but sometimes save doing case from GUI like tileset parameters saved in .tmx
Thats why bad workflow around class/type: #4018 (comment)
Confirmed here: #4018 (comment)

[eishiya]

In what way would would Import differ from Open?

If you just want to edit or otherwise look at a TSX tileset, you can Open it in Tiled. If you're looking to add a TSX tileset to an existing map, there's the Add Tileset button in the map's tilesets view. If you want to replace an existing tileset, there's Replace Tileset.

[ManPython]

It's regarding buttons where is export under/above tilesets tabs.
I missed map > add external - thx.
Anyway, then should be here map > import in menu and re-organisation to to divide parts regarding .tmx and .tsx to be more cognitive with this.
I'm referring import regarding many .tmx in case in one is added new tileset with .tsx then want apply to other files as .tmx
Sure.. ca do this by edit .tmx in editor but is hard job and this not always refreshing opened .tmx in TEditor, by this can be issue around override.

[bjorn]

I think there are multiple basic usability / discoverability issue here:

• The action "Add External Tileset" is only present in the "Map" menu and in the tileset selection dropdown (which is really only opened by people that use lots of tilesets). Probably the "New Tileset" button should be changed into a dropdown with two actions: select an existing tileset or create a new one. A possible issue with that is that "New Tileset" actually doesn't add the new tileset to the map. There's generally no need for this, since Tiled will add it automatically when you first use the tileset (which is partly why "Add External Tileset" is actually somewhat superfluous and possibly rarely used).

• The name "Add External Tileset" is confusingly verbose and probably could just be changed to "Add Tileset". I don't think "import" is the right name for this, though. That used to mean the tileset will be embedded, though at some point this naming was changed to "Embed Tileset" to be more explicit.

Actually I see we still have #2882 open regarding the "Add External Tileset" action's visibility.

[ManPython]

This is not so cognitive around UX I think.. as "view of dock" - can be here:
https://user-images.githubusercontent.com/531764/110925274-45054780-8323-11eb-9c29-a93f0990843f.png
..but as GUI and trigers location practice should be icon aroun dock.
The tab list with tilesets is like Menu > Window type as typical MDI apps have. More arrange functions (cascade, etc.).

Right.. open is one function, import as put in .tmx (more like include) is second function.
Open is more like include due external, and maybe Include is better, and import to embedded solution.