Add component index to home pages (#3334)

Author: devongovett

packages/@react-aria/slider/docs/useSlider.mdx

@@ -19,7 +19,7 @@ import Anatomy from './anatomy.svg';
 import ChevronRight from '@spectrum-icons/workflow/ChevronRight';
 
 ---
-category: Sliders
+category: Forms
 keywords: [slider, range, aria]
 after_version: 3.0.0-alpha.3
 ---

packages/@react-spectrum/slider/docs/RangeSlider.mdx

@@ -20,7 +20,7 @@ import {RangeSlider} from '@react-spectrum/slider';
 ```
 
 ---
-category: Sliders
+category: Forms
 after_version: 3.0.0-alpha.0
 ---
 

packages/@react-spectrum/slider/docs/Slider.mdx

@@ -20,7 +20,7 @@ import {Slider} from '@react-spectrum/slider';
 ```
 
 ---
-category: Sliders
+category: Forms
 after_version: 3.0.0-alpha.0
 ---