Make it easier to add more file extensions to an existing colorizer/language

[mohsen1]

Currently you need to create a VSCode extension to map extensions that are not listed under a language to an existing language. In most cases I want to map a certain extension to a certain language and it shouldn't be this hard. A simple JavaScript object in the editor settings should be enough.

Something like this:

{
  "fileExtensionMapping": {
    "md": ["markdown", "mkdown"],
    "ng": "html"
  }
}

[alexandrudima]

👍 We really need to allow configuration of language mode resolution

[alexandrudima]

fyi @bpasero

[bpasero]

👍 , maybe in combination with allowing per-language settings.

[bpasero]

#3612 for March