Implements #4048#7196
Syntax:
(global|local) variable_name =
(scalar_expression|vector_variable|array_expr|initializer_list)
array_expr := array(repeat, value)
initializer_list := (value, value, value, ...)
The type of the newly created variable is defined by the type
of the right hand side intitializer.
Newly declared variable must not override an existing variable.
Variable may be assigned with global|local expression, but its type
must not be changed.
Newly the assignment operator also accepts the same right hand expressions
as the global|local variable definition.
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