fix: missing array implementation

[MrPoll0]

• Structured index expression with bounds, integer index and subtype checking
• Tests for array validation (expression + codegen)
• Must specify index to access array
• Array is initialized to subtype default value on first value assigning (not on declare)
• Only single array index supported for now
• Restricted '[' and ']' from variable names
• Improved Array Index Dialog UI
• Disallowed empty inputs

[CLAassistant]

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