Syntax highlighting in doctest comments?

I've been using the Eval Plugin of HLS, which provides us with a pleasant alternative for REPL.
That plugin provides a way to evaluate (or execute some simple ghci-like commands such as `type`) codes in doctest style comment: `-- >>>`.
The result is appended as line comments right after the doctest comments.

In some situation, both of the inputs and outputs of doctest comments can be relatively long.
I think it might be useful if VSCode also highlights the contents inside the doctest comments and comments that immediately follow.

In short: currently, we have the following:


And it might be good if this becomes (with a less bright colour than in the standard code block):


If I understand correctly, there is a VSCode API to change text-decorations dynamically.
Or, perhaps this should be resolved upstream, i.e. might be reported to [JustusAdam/language-haskell](https://github.com/JustusAdam/language-haskell)?

Start by checking how HLS and the JustusAdam/language-haskell extension currently tokenize or decorate Haskell doctest comments, and review the VSCode text-decoration API mentioned in the issue. Determine whether the change belongs in HLS or upstream, then verify that doctest inputs and immediately following output comments receive subdued syntax highlighting.

Written by the indexing model from the issue text.