docs(material/core): list out pre-built themes (#29251)

Adds a table with all of the pre-built themes in the theming guide.

Fixes #29152.

Author: crisbeto

guides/getting-started.md

@@ -28,7 +28,7 @@ determine which features to include:
 
 1. Choose a prebuilt theme name, or "custom" for a custom theme:
 
-   You can choose from [prebuilt material design themes](https://material.angular.io/guide/theming#using-a-pre-built-theme) or set up an extensible [custom theme](https://material.angular.io/guide/theming#defining-a-theme).
+   You can choose from [prebuilt material design themes](https://material.angular.io/guide/theming#pre-built-themes) or set up an extensible [custom theme](https://material.angular.io/guide/theming#defining-a-theme).
 
 2. Set up global Angular Material typography styles:
 

guides/schematics.md

@@ -26,7 +26,7 @@ The Angular Material `ng add` schematic helps you set up an Angular CLI project
 
 - Ensure [project dependencies](./getting-started#step-1-install-angular-material-angular-cdk-and-angular-animations) are placed in `package.json`
 - Enable the [BrowserAnimationsModule](./getting-started#step-2-configure-animations) in your app module
-- Add either a [prebuilt theme](./theming#using-a-pre-built-theme) or a [custom theme](./theming#defining-a-custom-theme)
+- Add either a [prebuilt theme](./theming#pre-built-themes) or a [custom theme](./theming#defining-a-custom-theme)
 - Add Roboto fonts to your `index.html`
 - Add the [Material Icon font](./getting-started#step-6-optional-add-material-icons) to your `index.html`
 - Add global styles to

guides/theming.md

@@ -91,8 +91,28 @@ more about these terms):
 
 ##### Pre-built themes
 
-There are a number of color palettes available in `@angular/material` that can be
-used with the `primary` and `tertiary` options:
+Angular Material includes several pre-built theme CSS files, each with different palettes selected.
+You can use one of these pre-built themes if you don't want to define a custom theme with Sass.
+
+| Theme                  | Light or dark? | Specification                    |
+|------------------------|----------------|----------------------------------|
+| `azure-blue.css`       | Light          | Material Design 3                |
+| `rose-red.css`         | Light          | Material Design 3                |
+| `cyan-orange.css`      | Dark           | Material Design 3                |
+| `magenta-violet.css`   | Dark           | Material Design 3                |
+| `deeppurple-amber.css` | Light          | Material Design 2                |
+| `indigo-pink.css`      | Light          | Material Design 2                |
+| `pink-bluegrey.css`    | Dark           | Material Design 2                |
+| `purple-green.css`     | Dark           | Material Design 2                |
+
+These files include the CSS for every component in the library. To include only the CSS for a subset
+of components, you must use the Sass API detailed in [Defining a theme](#defining-a-theme) above.
+You can [reference the source code for these pre-built themes](https://github.com/angular/components/blob/main/src/material/core/theming/prebuilt) to see examples of complete theme definitions.
+
+##### Pre-defined palettes
+
+The pre-built themes are based on a set of pre-defined palettes that can be used with the `primary`
+and `tertiary` options:
 
 - `$red-palette`
 - `$green-palette`