Same function index shared with different functions

[clearloop]

when we got multiple external functions with the same content but different function names, the later ones will override the previous ones in the exports table in our parser, for example

/// addition
#[zink::external]
pub fn foo(x: i32, y: i32) -> i32 {
   x + y
}

/// addition
#[zink::external]
pub fn bar(x: i32, y: i32) -> i32 {
   x + y
}

while this is actually unexpectedly in development, e.g. duplicate code, we ban this behavior directly atm instead of supporting it, feel free to discuss on it!