feat(material/theming): Open up new APIs to access theme values

This PR opens up the following Sass APIs used to access theme values:
- `get-theme-version`: Gets the version of the theme object
- `get-theme-type`: Gets the type of theme (light or dark)
- `get-theme-color`: Gets a color from the theme
- `get-theme-typography`: Gets a typography value from the theme
- `get-theme-density`: Gets the density scale from the theme
- `theme-has`: Checks if the theme has information for the given theming
  system

src/material/_index.scss

@@ -142,7 +142,6 @@ list-density, list-base;
   $private-mdc-base-styles-query, $private-mdc-base-styles-without-animation-query,
   $private-mdc-theme-styles-query, $private-mdc-typography-styles-query;
 
-// New theming APIs, currently in development:
-@forward './core/theming/inspection' as private-* show private-get-theme-version,
-  private-get-theme-type, private-get-theme-color, private-get-theme-typography,
-  private-get-theme-density, private-theme-has;
+// New theming APIs:
+@forward './core/theming/inspection' show get-theme-version, get-theme-type, get-theme-color,
+  get-theme-typography, get-theme-density, theme-has;