In this patch, I tried to assign a useful reaction to ToggleBlockComment for stream comments.
There are two cases:
a.) Language has only stream comment available:
ToggleBlockComment toggles just the stream comment of the selection or line.
b.) Language provides stream comment AND block comment:
ToggleBlockComment performs undoStreamComment() only if the cursor or the complete selection is within a single stream comment.
Otherwise, the normal block comment reaction will be performed for the selected lines.