[DMN Designer] Data Types - Inline add action button

Change the behavior and tooltip for the inline add icon-button . Currently it converts the type to Structure before adding a row below. Instead, we want it to add another row without converting the type.

Acceptance criteria:

• Tooltip: "Add row below (Ctrl + B)"

Behavior - Clicking the inline add button:

• from a type defined as Structure, will add a field row below.
• from a Field row (within a Structure), will add another field row below.
• from a Simple type, such as "Person(string)", will add another row of the same type below.