• Added task to validate that produced .jar, -sources.jar, -javadoc.jar are effectively empty (contain only META-INF, no .class, .tasty, .sjsir .html, etc)
• Don't delegate scala3-library-bootstrapepd and scala3-library-sjs for doc tasks to scala-library-bootstrapped tasks - Fixes scala3-library javadoc contains duplicated scala-library documentation #24807
• Also don't delegate scala3-library-nonboostrapped
• Deduplicate settings used in all of the mentioned tasks

Piggy backed changes (small improvements unrelated directlly to the core of the PR):

• simplifiy fetchedScalaInstanceSettings - always use scalaVersion.value
• ensure that downloaded sbt-scala3-bridge uses the same version as used scalaVersion