[Feature request] Use default settings in code for executorMap settings

**Is your feature request related to a problem? Please describe.**
Setting custom executorMap settings requires the full map to be present in your vscode config, whether it's changed or not.

**Describe the solution you'd like**
I'd like the code to use default settings whenever the value is not found in settings.json. This could be done at runtime by determining the map using object spreading (ie `executorMap = {...defaultExecutorMap, ...vscodeExecutorMap}`).
This change would allow settings.json to only contain *changed* entries, rather than all of the entries.