Fix conflict between variable or property and parameter in variable setters

[D8H]

Context

• An identifier in a "Set variable value" action matches an extension scene variable and a parameter at the same time

Actual

• A parameter getter is generated as if it where a variable and it crashes at preview
• The event sheet displays a parameter icon for the variable field

Expected

• A scene variable getter is generated (as parameter can't be used in actions)
• The event sheet displays an extension scene variable icon for the variable field

Note that, in both cases, a non-fatal error will appear in the event sheet for the conflict with the parameter (the error message is not displayed anywhere because the VariableField don't display ExpressionValidator errors)