fix(material/dialog): dialog actions overlow and are unreachable

Fixes a bug in the Angular Material dialog  component where
buttons/actions are unreachable due to dialog overflowing
because of unspecified max-height for the mat-dialog-container
parent flexbox.

Fixes angular#24785

src/material/dialog/dialog.scss

@@ -10,6 +10,9 @@ $mat-dialog-content-max-height: 65vh !default;
 // Dialog button horizontal margin. This has been extracted from MDC as they
 // don't expose this value as variable.
 $mat-dialog-button-horizontal-margin: 8px !default;
+// Dialog container max height. This has been given a default value so the
+// flex-children can be calculated and not overflow on smaller screens.
+$mat-dialog-container-max-height: 95vh !default;
 
 // Note that we disable fallback declarations, but we don't disable fallback
 // values, because there are a lot of internal apps that don't include a proper
@@ -32,6 +35,8 @@ $mat-dialog-button-horizontal-margin: 8px !default;
     // The dialog container is focusable. We remove the default outline shown in browsers.
     outline: 0;
 
+    max-height: $mat-dialog-container-max-height;
+
     .mdc-dialog__container {
       transition-duration: var(--mat-dialog-transition-duration, 0ms);
     }