Add typed variable bindings to Anko

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What this task asks for

Add typed `var` declarations in Anko and enforce declared type constraints on assignment when TypedBindings is enabled. Add `var x: type = value` syntax to Anko for typed variable declarations. When the TypedBindings option is enabled, the VM enforces type constraints on assignment. When TypedBindings is disabled, typed declaration syntax still parses and executes, but constraint enforcement is not applied and assignments behave dynamically. Assignments to typed variables must match the declared type in any scope. Anko numeric literals are `int64` and `float64` by default. Declaring an unknown type must return an error containing `unknown type` or `undefined type`.