[Feature] Implement assignment to arrays based on index

[Luna-Klatzer]

Is there an existing proposal for this?

• [X] I have searched the existing issues

This feature does not exist in the latest version

• [X] I am using the latest version

Proposal

Implement assignment to arrays, which allows the user to assign to a specific index in an array like this:

var x: Array<num> = [1, 2, 3];

...

x[0] = 4;

x; // -> [4, 2, 3];

Exact behaviour / changes you want

• [x] Add support for assignments to index members of arrays.
• [ ] Add runtime error OutOfBoundsError which is thrown when the index assigned to is outside the array's length.
• [x] Add appropriate internal functionality and code generation to JavaScript and TypeScript.

[Luna-Klatzer]

Implemented by #677.

Out of bounds checking to be done in another task.