Improve autocompletion and errors according to variable types

[D8H]

• Add autocompletion with brackets access for structures and arrays.
• Improve error messages when brackets are empty.
• Fix autocompletion of variable parameters in function calls wrongly suggesting objects and functions.
• Only display relevant variables in autocompletion according to their type.
• Display an error when string, number or boolean variable is used and a structure or an array is expected and the other way around.