Add interpolator highlighting to VSCode

[Martoon-00]

Looks like the Haskell grammar in VSCode is extensible for things like this, so it would be nice to make parts of the interpolator highlighted.

For instance:

[int|sT|My text goes here #b{call a b c} |]
      \ yellow      \       \      \ normal code color 
                     \       \ some special color for the rendering mode and for braces
                      \ inherited from string