[flake8-pyi] Implement PYI051 (#6215)

## Summary
Checks for the presence of redundant `Literal` types and builtin super
types in an union. See [original
source](2a86db8271/pyi.py (L1261)).

This implementation has a couple of differences from the original. The
first one is, we support the `complex` and `float` builtin types. The
second is, when reporting diagnostic for a `Literal` with multiple
members of the same type, we print the entire `Literal` while `flak8`
only prints the `Literal` with its first member.
For example:
```python
from typing import Literal

x: Literal[1, 2] | int
```  
Ruff will show `Literal[1, 2]` while flake8 only shows `Literal[1]`.

```shell
$ ruff crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:4:18: PYI051 `Literal["foo"]` is redundant in an union with `str`
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:5:37: PYI051 `Literal[b"bar", b"foo"]` is redundant in an union with `bytes`
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:6:37: PYI051 `Literal[5]` is redundant in an union with `int`
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:6:67: PYI051 `Literal["foo"]` is redundant in an union with `str`
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:7:37: PYI051 `Literal[b"str_bytes"]` is redundant in an union with `bytes`
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:7:51: PYI051 `Literal[42]` is redundant in an union with `int`
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:9:31: PYI051 `Literal[1J]` is redundant in an union with `complex`
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:9:53: PYI051 `Literal[3.14]` is redundant in an union with `float`
Found 8 errors.
```

```shell
$ flake8 crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:4:18: Y051 "Literal['foo']" is redundant in a union with "str"
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:5:37: Y051 "Literal[b'bar']" is redundant in a union with "bytes"
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:6:37: Y051 "Literal[5]" is redundant in a unionwith "int"
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:6:67: Y051 "Literal['foo']" is redundant in a union with "str"
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:7:37: Y051 "Literal[b'str_bytes']" is redundantin a union with "bytes"
crates/ruff/resources/test/fixtures/flake8_pyi/PYI051.pyi:7:51: Y051 "Literal[42]" is redundant in a union with "int"
```

While implementing this rule, I found a bug in the `is_unchecked_union`
check. This is the new check.


1ab86bad35/crates/ruff/src/checkers/ast/analyze/expression.rs (L85-L102)

The purpose of the check was to prevent rules from navigating through
nested `Union`s, as they already handle nested `Union`s. The way it was
implemented, this was not happening, the rules were getting executed
more than one time and sometimes were receiving expressions that were
not `Union`. For example, with the following code:
 ```python
  typing.Union[Literal[5], int, typing.Union[Literal["foo"], str]]
 ```

The rules were receiving the expressions in the following order:
- `typing.Union[Literal[5], int, typing.Union[Literal["foo"], str]]`
     - `Literal[5]`
     - `typing.Union[Literal["foo"], str]]`

This was causing `PYI030` to report redundant information, for example:
 ```python
typing.Union[Literal[5], int, typing.Union[Literal["foo"],
Literal["bar"]]]
 ```
This is the `PYI030` output for this code:
```shell
PYI030 Multiple literal members in a union. Use a single literal, e.g. `Literal[5, "foo", "bar"]`
YI030 Multiple literal members in a union. Use a single literal, e.g.`Literal[5, "foo"]`
```

If I haven't misinterpreted the rule, that looks incorrect. I didn't
have the time to check the `PYI016` rule.

The last thing is, I couldn't find a reason for the "Why is this bad?"
section for `PYI051`.

Ref: #848 

## Test Plan

Snapshots and manual runs of flake8.
\

ruff.schema.json

@@ -2408,6 +2408,7 @@
         "PYI049",
         "PYI05",
         "PYI050",
+        "PYI051",
         "PYI052",
         "PYI053",
         "PYI054",