Scala3doc: extension methods are not grouped properly

[abgruszecki]

See https://scala3doc.virtuslab.com/pr-master/scala3/api/scala/opaques/array-ops/index.html.

Grouping extensions was based on positions. Since we implemented it, the implementation of extension methods was changed, so perhaps that is where the problem is?

[odersky]

The grouping should be based on the position of the leading parameter section. The leading parameter is the first parameter, except for right-associative methods, where it is the second parameter. (There's a parameter swap for right-associative operators when we go from collective extensions to internal extension methods). See method extensionParam in SymDenotations.scala.

The compiler also has code that depends on the grouping. See isLocalExtensionMethodRef in Typer.scala.

[pikinier20]

@abgruszecki Prevoiously we were groupping by position, but I see that currently we are groupping by DRI of extended symbol (which changed recently) which is not quite good, because in arrayOps extensions on IArray[ConcreteType] are groupped in our docs. I'm gonna make a fix for this.

[abgruszecki]

Reopening, the issues is still there.

[abgruszecki]

Correction: there's no bug on Scala3doc side, it merely duplicates the original source structure (which has a separate extension clause for each definition). My bad.