Color tokens for TypeScript and JavaScript inlay hints (#232)

VS Code 1.60 [1] (August 2021) introduced inlay hints for JavaScript and
TypeScript [2] (opt-in via `editor.inlayHints.enabled`), including new
color tokens to customize their appereance.
They have been added and adjusted to match Nord's theme style:

- `editorInlayHint.background` - the background color used for inline
  hint boxes.
- `editorInlayHint.foreground` - the foreground color used for inline
  hint boxes.

[1]: https://code.visualstudio.com/updates/v1_60
[2]: https://code.visualstudio.com/updates/v1_60#_inlay-hints-for-javascript-and-typescript

Closes GH-224

themes/nord-color-theme.json

@@ -48,6 +48,8 @@
     "editorHint.foreground": "#ebcb8b",
     "editorIndentGuide.background": "#434c5eb3",
     "editorIndentGuide.activeBackground": "#4c566a",
+    "editorInlayHint.background": "#434c5e",
+    "editorInlayHint.foreground": "#d8dee9",
     "editorLineNumber.foreground": "#4c566a",
     "editorLineNumber.activeForeground": "#d8dee9",
     "editorWhitespace.foreground": "#4c566ab3",