Compile parameter defaults as separate functions, not inlined expressions

When adding default arguments that can reference earlier parameters to an LLVM-backed compiler, emit each default as its own internal function taking the preceding parameters, and have call sites call it for omitted arguments. Copying the default expression into every call site expands forever at compile time when a default calls its own function (e.g. m <- f(n, 1) inside f); as a function it is ordinary runtime recursion, and -O3 inlines the small ones anyway. Evaluate written arguments in source order first (sort by span start), then fill inputs left to right so each default sees the values filled so far. Also watch for syntax collisions: a 'name <- value' named argument can shadow an existing 'Type <- [pack]' construction form, so pick one rule (name wins, parenthesize the other) consistently across packs and calls.