Adds a class `PubContext` with a fixed set of allowed values
Make it clear these values should not be changed casually

Fixed one inconsistency already: update_packages vs update_pkgs
Provide more information for verify calls
Eliminate `ctx_` prefix.

* Provide more information in PUB_ENVIRONMENT for `pub get/upgrade`

Should help diagnose and fix https://github.com/dart-lang/pub-dartlang-dart/issues/636

A more future-proof approach to accessing internal package name lint rule description details.

See: https://github.com/dart-lang/linter/issues/654

* Fix --preview-dart2 option handling for ios profile/release.

* Remove unused parameter

This allows `flutter run` to work on hosts that are IPv6-only.

In 77af1e5e, dart:vmservice_sky was
renamed to dart:vmservice_io.

* Add support for NDK discovery and add --prefer-shared-library option

We would like to be able to use native tools (e.g. simpleperf, gdb) with
precompiled flutter apps.  The native tools work much better with *.so
files instead of the custom formats the Dart VM uses by default.

The reason for using blobs / instruction snapshots is that we do not
want to force flutter users to install the Android NDK.

This CL adds a `--prefer-shared-library` flag to e.g. `flutter build
apk` which will use the NDK compiler (if available) to turn the
precompiled app assembly file to an `*.so` file.  If the NDK compiler is
not available it will default to the default behavior.

* Rebase, add test for NDK detection, augment flutter.gradle with @Input for flag

* Use InMemoryFileSystem for test

* Remove unused import

* Address some analyzer warnings

Creates a new (hidden) flutter command 'ide-config' that will create and/or update
existing .iml files and some files under the .idea directory, as well as
removing existing *.iml files and the .idea directory.

It also:

 * Adds *.iml to the .gitignore
 * Removes existing .iml files from the repo, and moves them to the
   packages/flutter_tools/ide_templates/intellij directory.
 * Adds a flag to ide-config ('--update-templates') that will take any new .iml
   files in the flutter tree and add them to the existing templates.
     - If --overwrite is also specified, then all existing templates will also
       be overwritten with the contents from the flutter tree, and any that have
       been deleted from the flutter tree will also be removed from the
       templates.
 * Added new run configurations for all existing app targets that will now also
   be automatically added to IntelliJ.
 * Setting up the environment also includes setting the coding style guidelines
   and the git VCS.
 * Note that after this PR lands, Flutter developers will need to run it once to
   re-create the .iml files and configuration files that have been removed.

After this PR lands, .iml files will no longer appear in the untracked files
section for git.

* tweak the text for the 'elements didnt reload' message

* review comments

* prefix items with a list char

* add a hostIsIde param instead of the isDaemonMode top-level function

* add a trailing comma

* executable.dart#main() depends on runner.dart#run()
* Refactor code such that non-commands don't depend on commands.

No code was actually changed in this PR - code was merely moved from
point A to point B.

* enable lint prefer_asserts_in_initializer_lists

* enable --assert-initializer

* Leave a version tag when creating project

* Generalize .version to .metadata

* Revert "Revert "fix --force-upgrade script; upgrade to the latest package versions (#12700)" (#12729)"

This reverts commit 7f0d4f4c.

* keep linter pinned at 0.1.35

This reverts commit 5b357500.

* fix updrade script; upgrade to the latest package versions

* exclude special dependencies from transitive closure

* fix stack trace handling in flutter_test due to stack_trace change

* change type on _emptyStackTrace

* Make clean command top level

Fixes https://github.com/flutter/flutter/issues/10783

* remove backwards

gen_snapshot loads all packages from single app kernel file.

Add hidden options --extra-front-end-options and --extra-gen-snapshot-options to flutter tool (#12219)

This CL introduces 2 hidden options to 'flutter build aot' and 'flutter run' for passing arbitrary arguments to front-end server and to gen_snapshot tool when building and running flutter app in --profile or --release modes.

The ability to pass arbitrary options simplifies various experiments, as it removes the need to change defaults and rebuild flutter engine for every tested configuration.

This makes command validation happen as part of `verifyThenRunCommand()`,
using a newly introduced protected method (`validateCommand()`) rather than
a `commandValidator` property (that subclasses were responsible for manually
invoking).

* Pin all dependencies ONCE AND FOR ALL

This replaces the secret `flutter update-packages --upgrade` with a destructive `flutter update-packages --force-upgrade` that actually goes and pins every dependency and transitive dependency in every flutter package to the same version.

* Add comments.

* round 3

* partially address comments

* merge

* review notes

* review

* review

* review

* round 2

* deal with null futures

* review

* review

* review

* review