Sort stream imports for pekko-stream modules

[He-Pin]

Motivation:
When I do code modification in pekko-stream related module, after a sortImports I have to revert all unrelated changes, which is very annoying.

Result:
Sort the imports in pekko-stream and pekko-stream-tests.

The sort-imports will cause problem when encounter #xxx and does not obey the #scala-fix:off/on too.

[He-Pin]

I updated the conf.

[mdedetrich]

Are you sorting this using Intellij?

[He-Pin]

@mdedetrich I'm using the sbt sortImports

[mdedetrich]

@mdedetrich I'm using the sbt sortImports

Nice work, this is looking good especially considering its not messing with the import org.apache.pekko style and we can add a check to make sure imports are sorted to the CI later. I just added one comment.

[mdedetrich]

Not critical but it also would be good to squash the chore: sort imports for pekko-stream-tests and chore: sort imports for pekko-stream into a single commit.

[laglangyue]

When merging to the main branch, all commits will be converted to a single commit, right？
I often submit multiple times, I just want to make sure if I made a mistake.

Not critical but it also would be good to squash the chore: sort imports for pekko-stream-tests and chore: sort imports for pekko-stream into a single commit.

[laglangyue]

LGTM

[mdedetrich]

When merging to the main branch, all commits will be converted to a single commit, right？
I often submit multiple times, I just want to make sure if I made a mistake.

So this is the whole "rebase and merge" vs "squash and merge" debate. Some people have different preferences, but this PR specifically is an exception because since its adding a format commit we want to add it .git-blame-ignore-revs so it doesn't turn up in git blame however we want to make sure that ONLY the formatting changes are added and not anything else.

So ideally for this PR you would have one commit that does all of the necessary changes i.e. 84fb5f8 and then another commit which applies sortImports and its this commit which gets added to https://github.com/apache/incubator-pekko/blob/main/.git-blame-ignore-revs.

Otherwise we ordinarily don't care too much about rebase + merge versus squash + merge, although if you are the kind of person that adds lots of minor commits then you should use squash + merge.

[He-Pin]

@laglangyue I will do a rebase later, it was in this style to make review easier.

[He-Pin]

Once this get merged, will follow up a .git-blame-ignore-revs pr.

[He-Pin]

@mdedetrich @pjfanning I would like to have this merged first:)

[mdedetrich]

lgtm

[He-Pin]

Let me merge with with another pr which ignores the commit.