Minor tweak, much better flow for Global Styles

## Prerequisites

- [X] I have searched for similar features requests in both open and closed tickets and cannot find a duplicate.
- [X] The feature is still missing in the latest stable version of Elementor ( Elementor Pro. )

**What problem is your feature request going to solve? Please describe.**
Widgets typography property defaults to Global Style. When you edit a typography property on a widget to override the Global Style, it fills the typography properties with the Global Styles instead of filling with 'Default'. This is not the ideal and here's why:

- You set globally all H2 headers to be { font-family: Comic Sans; font-size: 2em; letter-spacing: 2px }
- You override a single H2 to be { font-size: 1.6em } -- and no other changes
- One day you realize that Comic Sans is not a good call and want to change all H2 to be {font-family: Arial}
- So you adjust H2 styles globally to be Arial
- All H2 titles change to the new setting, except the one that you overriden (but at the time you just want to override the size locally, not the font-family)
- The catch is, when you edit a style that is globally defined, it fills all settings with the literal value instead of filling it with 'Default'

**Describe the solution you'd like**
When overriding Global Typography, make all values show up as "Default" (instead of literal "Comic Sans")

**Describe alternatives you've considered**
Everytime I edit an widget to override the global style, I set the font-family and others to "Default", because I know that if I don't do that, when I make a change globally in the future, it won't apply automatically

**Additional context**
Maybe this idea apply to other global styles and would be nice that all of them behaved in the same way. It's just that typography is the one that bite me all the time.