Extension methods can be exported by name

[Akirathan]

First part of #10258 - extension methods can be exported by name

Pull Request Description

Ultimately, we want to forbid the from ... export all syntax. This PR starts by providing a way to explicitly export extension and conversion methods by name.

Stdlib code will be modified in upcoming PR.

Important Notes

A single name can refer to multiple extension or conversion methods. Exports are not qualified. For example,

type My_Type
type Other_Type
My_Type.ext_method x = x
Other_Type.ext_method x = x

from project.Mod export ext_method

will export both My_Type.ext_method and Other_Type.ext_method.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• [x] The documentation has been updated, if necessary.
• [x] Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• [x] All code follows the Scala, Java, TypeScript, and Rust style guides. In case you are using a language not listed above, follow the Rust style guide.
• [x] Unit tests have been written where possible.

[JaroslavTulach]

There are four compilation failures IrUtilsTest.