Color token for debugged line shown in overview ruler (#214)

VS Code 1.52 [1] (November 2020) introduced the new
`editor.focusedStackFrameHighlightBackground` theme color token [2] to
highlight the currently focused debugged line in the overview ruler.
Additionally, the `editor.stackFrameHighlightBackground` key has been
added that is used to highlight the decoration in the overview ruler on
the right of the editor.
Both tokens using `nord10` to make them more conform with Nord's style.

[1]: https://code.visualstudio.com/updates/v1_52
[2]: https://code.visualstudio.com/updates/v1_52#_ui-improvements

Co-authored-by: Sven Greb <development@svengreb.de>

Closes GH-205

themes/nord-color-theme.json

@@ -64,6 +64,8 @@
     "editor.rangeHighlightBackground": "#434c5e52",
     "editor.wordHighlightBackground": "#81a1c166",
     "editor.wordHighlightStrongBackground": "#81a1c199",
+    "editor.stackFrameHighlightBackground": "#5e81ac",
+    "editor.focusedStackFrameHighlightBackground": "#5e81ac",
     "editorError.foreground": "#bf616a",
     "editorError.border": "#bf616a00",
     "editorWarning.foreground": "#ebcb8b",