DMN: UI enhancements for Data Type editor

User Story
As a practitioner I want to be able to:

• select an existing data type
• create a simple or structured data type
• create a “compound” (or complex) data type, easily.
  * 
expand/collapse views of compound data types, so that I can___
  * 
navigate between levels in a compound data type, so that I can___
• edit an existing data type
• remove an existing data type
  
…so that I can use the data type when creating a decision related asset.

Requested UI enhancements, based on user feedback from 7.4 implementation (keyboard shortcuts are covered in a separate Epic)

NESTING ISSUES ARE HIGH PRIORITY

• Fix Dropdown menu labeling (Structure)
• Weird tooltip on Structured row.
• It wasn’t clear wasn’t what was nested, and looking for drag-n-drop to nest and reorder.
• Finding “Structure” in the dropdown - was separate, blue and at the bottom. Terminology.
• Nested data types, - all 3 used the field already open, but confusion about adding additional rows. Kebab didn’t work so well. Terminology for kebab menu.
• Due to the icon at the top level and no icons at the second level, the indenting of second level items is not very clear for users. Make sure the nesting is very clear at a glance.
• Better way to add a new field that is always visible to the user and clear to use without having to go into a kabob menu

RELATED SAVE INTERACTIONS (Save, Delete, Remove)

• Inline editing of the content in the rows would make the experience nicer than having a whole row edit model
• - It's not obvious that you have to select the "check mark" to commit the change.
• After adding a new data type field, undo becomes available but instead of removing the field, it resets the field name and type to the defaults. Redo then becomes available but doesn't appear to do anything when clicked.

OTHER:

• “Constraint” link was confusing, but location was good.
• In the dialog, “Add” wasn’t found too well. (Bug adding a null constraint.)
• Questions around Save - should it not require Save at the row level.
• It feels unnatural to have to click the "Constraints" to open the Constraints modal.