chore: Use license file directly instead of symlinks

[spydon]

Description

Since you can't publish a package with a symlink referring outside of the package this turns all the LICENSE symlinks to real files.

Checklist

• The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs:, chore: etc).
• I have read the Contributor Guide and followed the process outlined for submitting PRs.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation and added dartdoc comments with ///, where necessary.
• I have updated/added relevant examples in example.

Breaking Change

• No, this is not a breaking change.

Related Issues

[Gustl22]

@spydon are you sure it doesn't work without the script?
But don't know if it concerns the repo or the package...
dart-lang/pub#2193

Edit: I'm wrong dart-lang/pub#2699

[spydon]

@spydon are you sure it doesn't work without the script?
But don't know if it concerns the repo or the package...
dart-lang/pub#2193

Edit: I'm wrong dart-lang/pub#2699

I think it possibly works to publish from Windows, but that's just because symlinks works differently there.

For the license file I don't think it matters much anyways since it never changes.

[Gustl22]

We should also add separate READMEs for each package, as they are symlinks, too, like done with Flutter packages. But we can do this in a separate Merge Request, if desired.