Allow using complex type as a map key

### What is wrong?
Currently, using a complex type as a map key is not allowed.
It'd be better to relax this restriction.

```python
struct MyStruct:
x: u256
y: u256


contract Foo:
s: Map
```

### How can it be fixed
New `codegen` allow this feature, so just removing the checking in `analyzer` would work if there is no bug in `codegen`.

Start by locating the analyzer check that rejects complex map-key types, then inspect the codegen path to confirm its existing support. Done means the analyzer no longer blocks the shown MyStruct map key and the codegen behavior remains correct; the issue does not name specific files or tests.

Written by the indexing model from the issue text.