Currently, for the shape of the local style we are using something like this:

		"style": {
			"color": {
				"text": "#00e"
			},
			"typography": {
				"lineHeight": 20,
				"fontSize": 12
			}
		}

While for global styles we were using the shape:

		"styles": {
			"color": "#00e",
			"line-height": 20,
			"font-size": 12
		}

We should use the same shape and this PR updates the global styles shape to be similar to what we had for local styles.

There is still one inconsistency for local styles we call "style" and for global styles, we call "styles". Should we update global styles to use "style"?

Besides this update we also perform smaller updates required to have a link color end to end implementation:
- We add a setting __experimentalGlobalStyles containing the full global styles required to show the defaults including user-set global styles.
- We unconditional include the default styles even if the theme does not has theme.json support. I guess even if the theme does not contain theme.json we may want to allow users to change the link color, and even change it globally and for that, we need a default even if for themes that don't have theme.json.

How has this been tested?

I added this after global to /lib/experimental-default-theme.json:

	"core/paragraph": {
		"styles": {
			"color": {
				"text": "#00e"
			},
			"typography": {
				"lineHeight": 20,
				"fontSize": 12
			}
		}
	}

I verified the following styles were output:

p {
	line-height: 20;
	font-size: 12;
	color: #00e;
}