When we package Flutter, we used to find the "current" tag (which is the version number) by starting at the revision we are building on and looking backwards in time to find the most recent tag. This causes problems on release builds when we failed to tag properly.

This PR makes the packaging script be more strict by requiring the given revision to itself have a tag, but only when we're publishing the result. When we're not publishing the result, it's more lenient, since otherwise we couldn't test packaging on non-release commits.

I also renamed ProcessRunnerException to PreparePackageException, since we were using that exception more generally than just for processes.

Adds SHA256 checksums to the released package database, in preparation for showing them on the download website. (I'll update the existing data by hand).

Fixes #28465

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

All temporary directory start with `flutter_` and have their random component separated from the name by a period, as in `flutter_test_bundle.YFYQMY`.

I've tried to find some of the places where we didn't cleanly delete temporary directories, too. This greatly reduces, though it does not entirely eliminate, the directories we leave behind when running tests, especially `flutter_tools` tests.

While I was at it I standardized on `tempDir` as the variable name for temporary directories, since it was the most common, removing occurrences of `temp` and `tmp`, among others.

Also I factored out some common code that used to catch exceptions that happen on Windows, and made more places use that pattern.

* Upgrade everything except matcher.
* Roll matcher (and test)
* Adjust tests that depend on flutter:test directly to depend on a shim
* Require use of package:test shim and remove other references to package:test

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

* Bump mockito to 3.0.0-beta

* Few fixes

* fix test

* Bump image

* Fix

* New packages update

* With matcher pinned

* No more typed

The new matcher package deprecates isInstanceOf which seems eggregious.

This changes the packaging tool to only set the remote URL instead of recreating the remote.

Recreating it was removing some metadata that identified the repo as having been cloned from the "real" repo, so flutter --version would report an unknown channel and source. This just sets the URL so that it looks like it came from GitHub.

I also fixed some incorrect comments, and made unzip work on platforms other than Windows (even though we don't really need it there yet).

Fixes #15518

This fixes the error handling for the packaging script so that it will properly report a failure exit code when it can't find the executable that it's looking for.

Added a test too.

We can't use .tar.xz on Mac because although it can unpack them on the command line (with tar), the "Archive Utility" that runs when you double-click on them just does some crazy behavior (it
converts it to a compressed cpio archive, and when you double-click on that, it converts it back to .tar.xz, without ever unpacking it!)

So, this changes the script to use .zip for Mac, and the files are about 220MB larger than they need to be. 

When uploading, gsutil is guessing wrong about our desired MIME types. This makes it explicit.

I wanted to run a "real command" as part of the test, but in the interest of fixing the build, I'm just removing the test.

There were some problems I introduced with the last PR for this. It passed the test, but failed in practice.

This adds tests for those failure cases, adds a "--help" and fixes the test so that it doesn't try and actually download MinGit as part of the Windows test.

I added package:platform as a dependency, so I did a force upgrade on the packages.

Also, re-enabling 'create package' in the cache warming code, now that #14448 is fixed.

This changes the publishing of archives so that it happens on the chrome_infra bots when they build a packaged branch instead of as part of the dev_roll process.

It uses the tagged version in the branch, and leaves the git repo that it clones checked out on the branch and hash used to build the package.

It updates metadata located at gs://flutter_infra/releases/releases_.json (where is one of macos, linux, or windows) once published, since it would be complex to do the proper locking to keep them all in one shared .json file safely.

A separate [change to the chrome_infra bots](https://chromium-review.googlesource.com/c/chromium/tools/build/+/902823) was made to instruct them to build packaged for the dev, beta, and release branches (but not master anymore).

* Revert "Reverting package changes until I can figure out how to fix Windows. (#14007)"

This reverts commit 6fda8ee8.

* Make prepare_package run on Windows

* Revert "Fixed output validation. (#14005)"

This reverts commit d84398db.

* Revert "Update package prep script to do async process execution and emit output as it happens. (#13918)"

This reverts commit b7169c1d.

 - Switches to async process execution, which now shows output as it happens instead of in chunks when the process completes
-  Now uses ProcessManager so that it may be mocked for the test.
- Adds in the download and install of mingit on Windows.
- Updated package dependencies because of added dependency on process package.

This reverts commit 765191e7.
because the updated packages cause a gradle build problem.

This adds our self-compiled copy of the MinGit executable (built from the flutter/git repo) to the archive when building an archive for Windows.

I also tweaked the internal API for prepare_package.dart so that there's a single entry point to build an archive.

A modern version of 7Zip (7za.exe) is now installed on the bots, this makes use of that.

XZ is about 50MB smaller, and it works on both Mac and Linux.

This is the first step in a two-step process of moving the package preparation step from a recipe in chrome_infra to a dart script in the flutter repo. This will make it easier to make changes to the process. The second step is to change the infra recipe to call this script.

In addition, I added a step to the packaging process to run flutter create for each type of template so that any pub dependencies of the templates get added to the cache that gets packaged (and thus users can run flutter create --offline and have it work).

Note that the actual packaging into a "tar" or "zip" file now happens here, so a developer could actually run this script on their machine to create a package.