Merge commit 'fetch_head'

Scala 3 port (com-lihaoyi#14)

@lihaoyi I have gone with Scala 3.5.0 here since that was the version I
have been porting Mill to.

I didn't see any testing procedure - so I used the Mill integration
tests to validate the override and scaladoc annotation inference is
working. (Also I could remove all the override modifiers I had
introduced in my Mill PR)

Note that now I made `moduledefs` a cross module in order to set the
right "species" of scala versions to build plugin against. This is
probably solved better with Cross2 but that needs to upgrade mill to
0.11.x which breaks the build in other ways I didn't want to touch

```
./millw -i resolve 'moduledefs'._
[1/1] resolve
moduledefs[2.13.14]
moduledefs[3.5.0]
```

```
./millw -i resolve 'moduledefs[2.13.14]'.plugin._
[1/1] resolve
moduledefs[2.13.14].plugin[2.13.0]
moduledefs[2.13.14].plugin[2.13.10]
moduledefs[2.13.14].plugin[2.13.11]
moduledefs[2.13.14].plugin[2.13.12]
moduledefs[2.13.14].plugin[2.13.13]
moduledefs[2.13.14].plugin[2.13.14]
moduledefs[2.13.14].plugin[2.13.1]
moduledefs[2.13.14].plugin[2.13.2]
moduledefs[2.13.14].plugin[2.13.3]
moduledefs[2.13.14].plugin[2.13.4]
moduledefs[2.13.14].plugin[2.13.5]
moduledefs[2.13.14].plugin[2.13.6]
moduledefs[2.13.14].plugin[2.13.7]
moduledefs[2.13.14].plugin[2.13.8]
moduledefs[2.13.14].plugin[2.13.9]
```

```
./millw -i resolve 'moduledefs[3.5.0]'.plugin._
[1/1] resolve
moduledefs[3.5.0].plugin[3.5.0]
```

tweak generated methods

fixes for upickle

fix scalajs scala3 compilation by removing duplicate HasDefaultParams…

… flag

fix-index-out-of-bounds

initial commit