Runtime validation for list mutation

[heshanpadmasiri]

We should detect illegal mutations of lists at runtime.

import ballerina/io;

public function main() {
    int[] arr = [4, 5, 6];
    any[] a = arr;
    a[2] = 1.2; // @panic
    io:println(a);
}

This would need #109

[heshanpadmasiri]

I think we should hold the type or the atomic type and use that to figure out the type of the member. Then do a type check against it when we store the value. As an optimization we can bring in the concept of exactness tracking from nBallerina, though I am not entirely sure we should port the implementation as is. I should work given all the target platforms (x86-64, aarch64 and wasm) are byte aligned, I am just not sure if it is too low level.