runtime(dtrace): handle DTrace probe highlighting before action blocks

runtime(dtrace): handle DTrace probe highlighting before action blocks

Recognize DTrace probe descriptions that are followed immediately by an
action block, such as:

    BEGIN{ trace(1); }
    syscall::open:entry{ trace(1); }

The fourth probe field now consumes the remaining non-whitespace text, and
the lookahead allows zero or more whitespace before the following token.

closes: #20560

Signed-off-by: Vladimír Marek <vlmarek13@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>