The `Mark Type` dialog is non-intuitive and needs improvement

[uxmal]

Although the basic functionality is there, it is hard to understand how to use it (#1286) Here are some suggestions:

Add a prompting text, such as

Enter the data type and name for the selected memory address. Use

• C syntax
• Rust syntax
• Reko Hungarian syntax

Followed by a textbox where the user can enter their declaration.

Also, make it possible to discover that a piece of data has a type, by hovering over it, you should see a tooltip with the data type for a given blob of memory. Naturally, selecting the Mark Type command should allow you to edit previously entered data. Finally, there should be a way to delete user-entered annotations (see #1218)