Don't fallback to the empty string for language in the DiffEditor to give Monaco a chance to deduce the langauge from paths

[SethBacaner]

Because originalLanguage and modifiedLanguage fallback to text in DiffEditor, Monaco will treat the contents as text and never try to infer the language from originalModelPath and modifiedModelPath. In Editor, language falls back to the empty string.

// Does not detect TypeScript.
<DiffEditor
    original="const a = 1;"
    modified="const a = 2;"
    originalModelPath="file.ts"
    modifiedModelPath="file.ts"
/>

// Has no problem detecting TypeScript.
<Editor
    value="const a = 1;"
    path="file.ts"
/>

This change updates DiffEditor to match the behavior of Editor.

[suren-atoyan]

Thank for your support @SethBacaner 🙌

Looks good, I'll test it and release a new version at the end of the week.

[SethBacaner]

@suren-atoyan 👋 did you ever get a chance to look at this further?