Add tuple lowering logic for assignment
Add tuple lowering logic for assignment

- When assigning tuples `(a0, ...) = (b0, ...)` generate a tuple of assignments `(a0 = b0, ...)`

- Given an expression statement on a tuple `(a0, ...);` generate a sequence of statements `a0; ...`

csyonghe/slang,csyonghe/slang,shader-slang/slang,csyonghe/slang,shader-slang/slang,shader-slang/slang