[manual_filter_map]: lint on matches and pattern matching

[y21]

Fixes #8010

Previously this lint only worked specifically for a very limited set of methods on the filter call (.filter(|opt| opt.is_some()) and .filter(|res| res.is_ok())). This PR extends it to also recognize matches! in the filter and pattern matching with if let or match in the map.

Example:

enum Enum {
  A(i32),
  B,
}

let _ = [Enum::A(123), Enum::B].into_iter()
  .filter(|x| matches!(x, Enum::A(_)))
  .map(|x| if let Enum::A(s) = x { s } else { unreachable!() });

Now suggests:

-  .filter(|x| matches!(x, Enum::A(_))).map(if let Enum::A(s) = x { s } else { unreachable!() })
+  .filter_map(|x| match x { Enum::A(s) => Some(s), _ => None })

Adding this required a somewhat large change in code because it originally seemed to be specifically written with only method calls in the filter in mind, and matches! has different behavior in the map, so this new setup should make it possible to support more "generic" cases that need different handling for the filter and map calls.

changelog: [manual_filter_map]: lint on matches and pattern matching (and some internal refactoring)

[rustbot]

r? @Alexendoo

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[Alexendoo]

Whoops, forgot to submit these 👀

[y21]

oops, forgot to bless the tests

[Alexendoo]

Thanks, looks good!

@bors r+

[bors]

📌 Commit 648d1ae has been approved by Alexendoo

It is now in the queue for this repository.

[bors]

⌛ Testing commit 648d1ae with merge 0b63e95...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Alexendoo
Pushing 0b63e95 to master...