Add support for flutter shaders

[YaroCabbage]

What does this change?

Flutter has had shader support for quite some time now. However, this package does not implement working with them. This PR aims to solve this problem.

I had to make this addition quickly, perhaps it is too rough, but still there was an attempt to do the maximum. I apologize for not creating an issue.

I added support even for what Flutter itself most likely has not implemented yet - flavor for shaders, but nevertheless. According to the settings, I implemented an almost complete copy of regular assets. It would be possible to simply pass shaders to the asset generator, but I decided to make a copy - perhaps this is excessive.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• Make sure to open a GitHub issue as a bug/feature request before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
  • Ensure the tests (melos run test)
  • Ensure the analyzer and formatter pass (melos run format to automatically apply formatting)
• Appropriate docs were updated (if necessary)

[AlexV525]

Just a quick look on my phone without reviewing generators implementation.

[YaroCabbage]

Just a quick look on my phone without reviewing generators implementation.

Fixed @AlexV525

[AlexV525]

Just had a complete review of the request.

I had to make this addition quickly, perhaps it is too rough, but still there was an attempt to do the maximum.

but I decided to make a copy - perhaps this is excessive.

Indeed. Shaders are mostly a sub-implementation to the assets so far. We may have some abstractions so assets and shaders can use both. However, we can also use the assets generator for shaders by tweaking some parameters. These APIs are just internally used so that we can refactor them anytime.