Work towards https://github.com/flutter/flutter/issues/157819. **No behavior changes as a result of this PR**.
Based on a proof of concept by @jonahwilliams (https://github.com/flutter/flutter/pull/157818).
The existence of this flag (which for the time being, defaults to `true`) implies the following:
1. The (legacy, deprecated) `.flutter-plugins` file is not generated:
https://docs.flutter.dev/release/breaking-changes/flutter-plugins-configuration
2. The (legacy, deprecated) `package:flutter_gen` is not synthetically generated:
https://github.com/flutter/website/pull/11343
(awaiting website approvers, but owners approve this change)
This change creates `useImplicitPubspecResolution` and plumbs it through as a required variable, parsing it from a `FlutterCommand.globalResults` where able. In tests, I've defaulted the value to `true` 100% of the time - except for places where the value itself is acted on directly, in which case there are true and false test-cases (e.g. localization and i10n based classes and functions).
I'm not extremely happy this needed to change 50+ files, but is sort of a result of how inter-connected many of the elements of the tools are. I believe keeping this as an explicit (flagged) argument will be our best way to ensure the default behavior changes consistently and that tests are running as expected.
For the necessary background knowledge, see the flutter.dev content on [Resolution-aware image assets](https://docs.flutter.dev/ui/assets/assets-and-images#resolution-aware) and [Conditional bundling of assets based on app flavor](https://docs.flutter.dev/ui/assets/assets-and-images#conditional-bundling-of-assets-based-on-app-flavor) if you don't have a basic understanding of these features.
Fixes https://github.com/flutter/flutter/issues/151813 by using unique temporary directories, per asset file, for transformations. Currently, only a single directory is used and the name of the temporary files was based only on the basename of files. This means that `assets/image.png` and `assets/2x/image.png` would share an output path (`<temp dir path>/image.png`), causing a race. If this quick and rough explanation is a bit confusing, the original issueâ#151813âprovides a full repro and correct identification of the exact cause of the failure that can occur in the asset transformation process.
