[BUG] No hot reloading for custom function file

[itsxallwater]

Describe the bug
If you are using the Custom functions and subroutines functionality of the extension and you make a change to the file you have configured, IntelliSense is not detecting the change and rebuilding the language definition on the fly. You have to reload the VS Code instance or change the value in the settings and re-introduce to trigger the IntelliSense to rebuild.

To Reproduce
Steps to reproduce the behavior:

1. Add a custom functions file to your config.
2. Begin typing one of the function names from the config to observe IntelliSense's suggestion.
3. Make a change to the file to tweak a function name, add a new function, etc.
4. Begin typing the new function name and observe IntelliSense does not make the suggestion.

Expected behavior
Ideally we can detect the file system change of the config record and update IntelliSense on the fly without forcing a reload.