Implement ```BitwiseXOR``` which takes two binary string literal type and returns a binary string that represents the bitwise XOR of S1 and S2
For example:
```typescript
BitwiseXOR<'0','1'> // expect '1'
BitwiseXOR<'1','1'> // expect '0'
BitwiseXOR<'10','1'> // expect '11'
```
