Add a new `BuildTargets` class that provides commonly used build targets. And avoid importing files from `build_system/targets` except from the top level entrypoints or from top level commands.
Also move `scene_importer.dart` and `shader_compiler.dart` into `build_system/tools` because they are not `Target` classes, but wrapper for certain tools.
With this change, we can ignore all files in `build_system/targets` internally and make PR #142709 easier to land internally. See cl/603434066 for the corresponding internal change.
Related to:
https://github.com/flutter/flutter/pull/142709https://github.com/flutter/flutter/issues/142041
Also note that I have opted to add a new variable in `globals.dart` for `BuildTargets` in this PR, but I know that we are trying to get rid of globals. Several alternatives that I was considering:
1. Add a new field in `BuildSystem` that returns a `BuildTargets` instance. Since `BuildSystem` is already in `globals`, we can access build targets using `globals.buildSystem.buildTargets` without adding a new global variable.
2. Properly inject the `BuildTargetsImpl` instance from the top level `executable.dart` and top level commands.
Let me know if you want me to do one of the above instead. Thanks!
Refactors `ShaderTarget` to make it opaque as to whether it's using Impeller or SkSL and instead has it focus on the target platform it's generating for.
ImpellerC includes SkSL right now whether you ask for it or not.
The tester target also might need SkSL or Vulkan depending on whether `--enable-impeller` is passed.
