Revert "Changes the offset computation to first item for RenderSliverMainAxisGroup" (#154688) (#168450)

This PR reverts commit 8cc862c7270ef911eabb9aba932dca7ec7c33f0d

I also added a regression test for
https://github.com/flutter/flutter/issues/167801 so that we do not break
that again when revisiting the issue that is reopened.

Fixes https://github.com/flutter/flutter/issues/167801
Reopens https://github.com/flutter/flutter/issues/154615

*List which issues are fixed by this PR. You must list at least one
issue. An issue is not required if the PR fixes something trivial like a
typo.*

*If you had to change anything in the [flutter/tests] repo, include a
link to the migration guide as per the [breaking change policy].*

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
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<!-- Links -->
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[test-exempt]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md
[Features we expect every widget to implement]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
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[Discord]:
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---------

Co-authored-by: Victor Sanni <victorsanniay@gmail.com>
https://dart.googlesource.com/external/github.com/flutter/flutter/+/2eeb6af6e73a7d4c5a720aaf2099f702cb23546d
diff --git a/DEPS b/DEPS
index 3a9fc6d..4f25995 100644
--- a/DEPS
+++ b/DEPS
@@ -237,7 +237,7 @@
 deps = {
   'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '69428c35cf673b18afb3bfd97c952d3c44f60958',
 
-  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '82e00c87c80c433581323ae8f84eac6013435b67',
+  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '2eeb6af6e73a7d4c5a720aaf2099f702cb23546d',
 
   'flutter/engine/src/flutter/third_party/depot_tools':
   Var('chromium_git') + '/chromium/tools/depot_tools.git' + '@' + '580b4ff3f5cd0dcaa2eacda28cefe0f45320e8f7',
diff --git a/commits.json b/commits.json
index 1c9932a..d12478c 100644
--- a/commits.json
+++ b/commits.json
@@ -1,4 +1,4 @@
 {
-  "flutter":"82e00c87c80c433581323ae8f84eac6013435b67",
+  "flutter":"2eeb6af6e73a7d4c5a720aaf2099f702cb23546d",
   "flutter/engine/src/flutter/third_party/dart":"69428c35cf673b18afb3bfd97c952d3c44f60958"
 }
\ No newline at end of file