Decide what to do with run-tests.sh and similar scripts and tools in dist builds

Problem/Motivation

In #3067979: Exclude test files from release packages we removed tests from the dist build of drupal/core to reduce package size on disk, reduce bandwidth usage, and improve the situation with Package Manager and automatic updates.

run-tests.sh and various development tools are still available in the dist build. This issue exists to clean those up further.

Steps to reproduce

Install a dist build of drupal/core
Execute run-tests.sh
Watch it fail

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet