Fixes https://github.com/flutter/flutter/issues/127090.
https://github.com/flutter/flutter/pull/122505 did a few things to speed up the first asset load that a flutter app performs. One of those things was to not include the main asset in its own list of variants in the asset manifest. The idea was that we know that the main asset always exists, so including it in its list of variants is a waste of storage space and loading time (even if the cost was tiny).
However, the assumption that the main asset always exists is wrong. From [Declaring resolution-aware image assets](https://docs.flutter.dev/ui/assets-and-images#resolution-aware), which predates https://github.com/flutter/flutter/pull/122505:
> Each entry in the asset section of the pubspec.yaml should correspond to a real file, with the exception of the main asset entry. If the main asset entry doesnât correspond to a real file, then the asset with the lowest resolution is used as the fallback for devices with device pixel ratios below that resolution. The entry should still be included in the pubspec.yaml manifest, however.
For example, it's valid to declare `assets/image.png` as an asset even if only `assets/3x/image.png` exists on disk.
This fix restores older behavior of including a main asset as a variant of itself in the manifest if it exists.
This fix also includes a non-user-visible behavior change:
* `"dpr"` is no longer a required field in the asset manifest's underlying structure. For the main asset entry, we do not include `"dpr"`. It makes less sense for the tool to decide what the default target dpr for an image should be. This should be left to the framework.
The global packages path could cause tests to fail when it would be overriden to unexpected (in test setup) values. Remove most usage and make it a configuration on buildInfo, along with most other build information. Cleanup the asset builder to require the .packages path and the resident runners to no longer require it, since they already have the information in build_info.
It needs to stick around for the fuchsia deps we do not control.
Filled #60232 for remaining work.
* Update project.pbxproj files to say Flutter rather than Chromium
Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.
* Update the copyright notice checker to require a standard notice on all files
* Update copyrights on Dart files. (This was a mechanical commit.)
* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.
Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).
* Clean up the copyrights in non-Dart files. (Manual edits.)
Also, make sure templates don't have copyrights.
* Fix some more ORGANIZATIONNAMEs
...because otherwise, processes that think they're manipulating your
filesystem will be doing crazy things the test is ignoring, leading to
(at best) failures and (at worst) flakes or disk corruption.
