Fix semantic rules for forward references in local functions

[JohnnyPol]

Forward declaration enforcement for local functions

• Dana's specification (§1.3.2 – Δομικές μονάδες) states that if a local function calls another local function defined later in the same scope, that called function must either be defined earlier or declared beforehand using decl.
• In our case, we applied the first option: we reordered the local function definitions so that any function is defined before it is used.

Therefore, in the Dana programs, we moved the definition of the swap function above other functions (such as quicksort) that call it.