[mlir] fix LLVM type converter for structs (#73231)

Existing implementation of the LLVM type converter for LLVM structs
containing incompatible types was attempting to change identifiers of
the struct in case of name clash post-conversion (all identified structs
have different names post-conversion since one cannot change the body of
the struct once initialized). Beyond a trivial error of not updating the
counter in renaming, this approach was broken for recursive structs that
can't be made aware of the renaming and would use the pre-existing
struct with clashing name instead.

For example, given

`!llvm.struct<"_Converted.foo", (struct<"_Converted.foo">, f32)>`

the following type

`!llvm.struct<"foo", (struct<"foo", index>)>`

would incorrectly convert to

```
!llvm.struct<"_Converted_1.foo",
             (struct<"_Converted.foo",
	             (struct<"_Converted.foo">, f32)>)>
```

Remove this incorrect renaming and simply refuse to convert types if it
would lead to identifie...