[Dialog] Add dialog with close button to demos

[rfbotto]

• I have followed (at least) the PR section of the contributing guide.

Closes #13520

[oliviertassinari]

@rfbotto I have pushed the approach one step further. Let me know what you think :)

[eps1lon]

I don't think we should add demos the go against material guidelines.

It might be especially confusing since close icons for fullscreen dialogs are located on the left while this one is on the right.

[oliviertassinari]

@eps1lon What would you change?

spec

google calendar

[eps1lon]

Well google engineers are also extending their designers decisions. This settles it for me then WRT to close icon.

I guess the important part here is that there would be no close action without the icon. The demo should reflect that. So replace the cancel action with something else so that the close action is not ambiguous.

[rfbotto]

@oliviertassinari Prefer it much more the way you did. Much cleaner and readable👍 Plus, i like the change to the demos buttons, makes them much more prominent. When it comes to the google material guidelines, as long as we make clear that we are getting away from the specification by allowing the customisation of the default behaviour, it should be okay, no?

[oliviertassinari]

@eps1lon Points taken. I have removed the close button in the footer (one way to do it) add I have added warnings about the non-material demos (to remove the ambiguity) following your feedback.