Code Highlighting in Editor

[FabrizioBrancati]

Is your feature request related to a problem? Please describe.
We would like to have a code highlighter in the Editor.

Describe the solution you'd like
We should use AppKit to add this feature. Currently, it would be good to just support the JSON format.
We can also add a Format button near the Import button, to automatically format the code. Also, we can set the editor border to red, if the format is wrong, but this will not change the ability to actually save the request (in case the user wants to send a malformed json).

Describe alternatives you've considered
None.

Additional context
None.

[gaetanomatonti]

We could use Sourceful.
It currently does not support JSON lexing, but we could contribute opening a PR.
UITextView and NSTextView subclassed are provided for custom syntax highlighting – a SwiftUI UIViewRepresentable is also provided.

[FabrizioBrancati]

@gaetanomatonti I agree, we can open some PRs to add more languages support 😉