runtime(rst): Fix doctest block syntax

runtime(rst): Fix doctest block syntax

A doctest block usually spans multiple lines, e.g.

>>> print('this is a Doctest block')
this is a Doctest block

Remove ``oneline`` argument to syntax region as this requirement is not
met.  Consequently, also remove ``display`` as the prerequisite (the
syntax region is on a single line) is no longer met.

----

Recognise '>>>' inside doctest blocks

Recognise subsequent '>>>' prompts in doctest blocks, e.g.

>>> print('this is a Doctest block')
this is a Doctest block
>>> print('this is a second Doctest block')
this is a second Doctest block
A doctest block usually spans multiple lines, e.g.

>>> print('this is a Doctest block')
this is a Doctest block

related: #18566

Signed-off-by: Kirk Roemer <91125534+kirk-roemer@users.noreply.github.com>
Signed-off-by: Marshall Ward <marshall.ward@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>