[Dialog] By default, actions display left-aligned

[andrewseguin]

Material spec shows that actions appear end-aligned by default, but our dialog actions do not. We do have an align SCSS rule but it is undocumented.

I propose that we should be default right-align the actions. If this ends up being too big of a change for internal tests, then we should at least bring more awareness to the option in our docs.

[mrmokwa]

A new MatDialogConfig property, which we could change the default button alignment would be nice. Something like:

{
   provide: MAT_DIALOG_DEFAULT_OPTIONS
   useValue: {
      buttonAlignPosition: 'end',
      restoreFocus: false 
   }
}

[crisbeto]

Closing because in M3 they're displayed to the right.