[useless_vec]: add more tests and don't lint inside of macros

[y21]

Closes #11084.

I realized that the fix I added in #11081 itself also causes an error in a suggestion when inside of a macro. Example:

macro_rules! x {
  () => {
    for _ in vec![1, 2] {}
  }
}
x!();

Here it would suggest replacing vec![1, 2] with [x!()], because that's what the source callsite is (reminder: it does this to get the correct span of x!() for code like for _ in vec![x!()]), but that's wrong when inside macros, so I decided to make it not lint if the whole loop construct is inside a macro to avoid this issue.

changelog: [useless_vec]: add more tests and don't lint inside of macros

r? @Alexendoo since these were your tests, I figured it makes most sense to assign you

[Alexendoo]

Great, thanks!

@bors r+

[bors]

📌 Commit b4549c5 has been approved by Alexendoo

It is now in the queue for this repository.

[bors]

⌛ Testing commit b4549c5 with merge 3f4e599...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Alexendoo
Pushing 3f4e599 to master...