Add something similar to dash:singleLine

[HolgerKnublauch]

dash:singleLine (https://datashapes.org/constraints.html#SingleLineConstraintComponent) can be used to specify that string values must not contain line breaks. This is commonly used for things like labels or ID strings.

While this can be expressed with sh:pattern, it is better to have an explicit boolean for this. For example, user interface builders can determine whether they should display a textfield vs a textarea.

[HolgerKnublauch]

In the Feb 24 meeting the WG accepted this feature into core, but marked as "At risk" which means that the WG will revisit the inclusion of this feature when it has gathered more evidence about the actual need. In a nutshell, the concern is where to draw the line and whether adding too many little features will open the floodgates.