Make BuildInfo plugin to be a drop-in replacement for sbt-buildinfo

[Awethon]

While the Mill's version has the basic functionality of sbt-buildinfo, it's not enough to be able to replace sbt for projects that use sbt-buildinfo with additional options:

BuildInfoOption.ToJson
BuildInfoOption.BuildTime
BuildInfoOption.Traits
BuildInfoOption.PackagePrivate

These options are lacking from Mill's BuildInfo and BuildInfoOption.Traits is the most painful of them not to have as we have internal libraries that accept BuildInfo trait as a parameter.

[lefou]

Can you please provide some documentation of the envisioned features?

[Awethon]

ToJson - returns json view of a BuildInfo (as a string)
https://github.com/sbt/sbt-buildinfo?tab=readme-ov-file#buildinfooptiontojson
impl: https://github.com/sbt/sbt-buildinfo/blob/develop/src/main/scala/sbtbuildinfo/ScalaRenderer.scala#L20-L43

BuildTime - adds build time to the Map of BuildInfo
https://github.com/sbt/sbt-buildinfo?tab=readme-ov-file#buildinfooptionbuildtime
impl: https://github.com/sbt/sbt-buildinfo/blob/develop/src/main/scala/sbtbuildinfo/BuildInfo.scala#L18-L30

Traits - makes BuildInfo to extend already existing traits by providing canonical names of them (BuildInfoOption.Traits("com.organization.MyTrait", "com.organization.MyTrait2"))
https://github.com/sbt/sbt-buildinfo?tab=readme-ov-file#buildinfooptiontraits
impl: https://github.com/sbt/sbt-buildinfo/blob/develop/src/main/scala/sbtbuildinfo/ScalaCaseClassRenderer.scala#L7-L8

PackagePrivate - makes BuildInfo package private using buildInfoPackage field to set a package scope
https://github.com/sbt/sbt-buildinfo?tab=readme-ov-file#buildinfooptionpackageprivate
impl: https://github.com/sbt/sbt-buildinfo/blob/develop/src/main/scala/sbtbuildinfo/ScalaRenderer.scala#L122-L125