[ty] print diagnostics with fully qualified name to disambiguate some cases (#19850)

There are some situations that we have a confusing diagnostics due to
identical class names.

## Class with same name from different modules

```python
import pandas
import polars

df: pandas.DataFrame = polars.DataFrame()
```

This yields the following error:

**Actual:**
error: [invalid-assignment] "Object of type `DataFrame` is not
assignable to `DataFrame`"
**Expected**:
error: [invalid-assignment] "Object of type `polars.DataFrame` is not
assignable to `pandas.DataFrame`"

## Nested classes

```python
from enum import Enum

class A:
    class B(Enum):
        ACTIVE = "active"
        INACTIVE = "inactive"

class C:
    class B(Enum):
        ACTIVE = "active"
        INACTIVE = "inactive"
```

**Actual**:
error: [invalid-assignment] "Object of type `Literal[B.ACTIVE]` is not
assignable to `B`"
**Expected**:
error: [invalid-assignment] "Object of type
`Literal[my_module.C.B.ACTIVE]` is not assignable to `my_module.A.B`"

## Solution

In this MR we added an heuristics to detect when to use a fully
qualified name:
- There is an invalid assignment and;
- They are two different classes and;
- They have the same name

The fully qualified name always includes:
- module name
- nested classes name
- actual class name

There was no `QualifiedDisplay` so I had to implement it from scratch.
I'm very new to the codebase, so I might have done things inefficiently,
so I appreciate feedback.

Should we pre-compute the fully qualified name or do it on demand? 

## Not implemented

### Function-local classes

Should we approach this in a different PR?

**Example**:
```python 
# t.py
from __future__ import annotations


def function() -> A:
    class A:
        pass

    return A()


class A:
    pass


a: A = function()
```

#### mypy

```console
t.py:8: error: Incompatible return value type (got "t.A@5", expected "t.A")  [return-value]
```

From my testing the 5 in `A@5` comes from the like number. 

#### ty

```console
error[invalid-return-type]: Return type does not match returned value
 --> t.py:4:19
  |
4 | def function() -> A:
  |                   - Expected `A` because of return type
5 |     class A:
6 |         pass
7 |
8 |     return A()
  |            ^^^ expected `A`, found `A`
  |
info: rule `invalid-return-type` is enabled by default
```

Fixes astral-sh/ty#848

---------

Co-authored-by: Alex Waygood <[email protected]>
Co-authored-by: Carl Meyer <[email protected]>

Author: 3 people