Handling custom functions in visual studio code lg extension

[chrimc62]

Tool

Name: LGVScodeExt

Describe the problem

The tool doesn't work very well when you have added custom functions in that they are always treated as an error.

Describe the solution you'd like

It would be great if the options for the extension let you register custom functions.

Describe alternatives you've considered

At the very least coloring a missing function definition in a different way as a warning would let you distinguish between things like syntax errors and custom functions.

Additional context

There are custom functions today in the forms generator and also in the conditions for triggers.

[enhancement]