Introduce custom definition language for monaco editor to get better highlighting in documentation

[beikov]

The syntax highlighting in the function suggestion and hover box are non-optimal i.e. a question mark is treated as invalid token. We need to define a definition language that describes signatures and define a color scheme for that.

The definition language could look like this:

parseDefinition: definition EOF;
definition: functionDefinition | varDefinition;
varDefinition: typeDeclaration identifier;
functionDefinition: typeDeclaration functionName LP functionArguments RP;
functionArguments: (functionArgument (COMMA functionArgument QM?)* (COMMA functionVarArgument)?)?
functionArgument: typeDeclaration identifier;
functionVarArgument: typeDeclaration DOT DOT DOT identifier;
functionName: identifier;
typeDeclaration: identifier (LB identifier RB)?;