Introduce new interface NamedExecutable that associates a name, a
payload and an Executable.

This was introduced to help colocate test's diplayName, payload, and
testExecutor in one place. Concrete usage of this interface is in the
next commit.

Issue: junit-team#3261

Introduce two methods in the class DynamicTest to generate a stream of
DynamicTests from a Stream/Iterator of NamedExecutables.

Instead of passing an inputStream, a displayNameGenerator and a
testExecutor separately, these two additional methods will allow you
to pass one Iterator/Stream of a NamedExecutable.

Unlike the Named interface, the NamedExecutable can colocate assertion
callbacks in one container using the execute method.

Issue: junit-team#3261

Write new changes to the release notes for 5.11M1 and add a simple demo
in DynamicTestsDemo.

Issue: junit-team#3261