feat!(menu): Implemented new Menu API

This is a complete rehaul of the menu components to hopefully be a lot
easier to use. Here's a quick diff representing the changes:

```diff
 import { render } from "react-dom";
-import { DropdownMenu } from "@react-md/menu";
+import { DropdownMenu, MenuItem } from "@react-md/menu";

 const App = () => (
-  <DropdownMenu
-    id="example-dropdown-menu"
-    items={[
-      { onClick: () => console.log("Clicked Item 1"), children: "Item 1" },
-      { onClick: () => console.log("Clicked Item 2"), children: "Item 2" },
-      { onClick: () => console.log("Clicked Item 3"), children: "Item 3" },
-    ]}
-  >
-    Dropdown
+  <DropdownMenu id="example-dropdown-menu" buttonChildren="Dropdown">
+    <MenuItem onClick={() => console.log("Clicked Item 1")}>Item 1</MenuItem>
+    <MenuItem onClick={() => console.log("Clicked Item 2")}>Item 2</MenuItem>
+    <MenuItem onClick={() => console.log("Clicked Item 3")}>Item 3</MenuItem>
   </DropdownMenu>
 );
```

New Functionality

- App-wide `Menu` behavior can be configured using the
  `MenuConfigurationProvider` or `menuConfiguration` prop on the
  `Layout` component
- The focus behavior in menus can be disabled with the new
  `disableFocusOnMount` and `disableFocusOnUnmount` props
- Menus have built-in support for rendering as a `Sheet` on mobile
  devices by setting `renderAsSheet="mobile"` on the `DropdownMenu`,
  `Menu`, `MenuConfigurationProvider`, or
  `Layout.menuConfiguration.renderAsSheet`
  - `rendeAsSheet` can also be set to `true` if you want to render all
    menus as sheets for some reason.
  - the sheets can be configured to have an optional `header` and
    `footer` as well
- `Menu` visibility can be controlled by child components of the
  `DropdownMenu` or `Menu` components using the new `useMenuVisibility`
  hook that provides the `visible` state and a `setVisible` function
- Built-in support for hoverable menus using the new `MenuBar` component

New Components

- `MenuItemFileInput` - a wrapper for the `<input type="file">` that
  works within `Menu` components (`@react-md/form`)
- `MenuItemTextField` - a wrapper for the `TextField` component that
  works within `Menu` components (`@react-md/form`)
- `MenuItemGroup` - a small wrapper for the `List` component that
  requires an `aria-label` and sets its `role` to `"group"`. This is
  just a convenience component for rendering `MenuItemRadio` components
  with other `MenuItem`s while maintaining accessibility
  (`@react-md/menu`)
- `MenuConfigurationProvider` - a new context provider to override menu
  behavior like rendering sheets.
- `MenuBar` - a new component that allows the child `DropdownMenu`
  components to gain visibility on hover after clicking one of the menus
  once. The menus can gain visibility on hover immediately if you
  provide a `hoverTimeout={0}` to the `MenuBar`.
  - The `MenuBar` also integrates some keyboard movement behavior
    following the [menubar spec](https://www.w3.org/TR/wai-aria-practices/#menu)

BREAKING CHANGE: The `DropdownMenu` component no longer accepts a list
of `items` and instead the `children` should be the `MenuItem`
components.

BREAKING CHANGE: The `useContextMenu` now returns an object instead of an
ordered list.

BREAKING CHANGE: The `DropdownMenuItem` component is no longer required
for nested dropdown menus and is an "internal" component instead that
shouldn't really be used.

BREAKING CHANGE: The `DropdownMenu` component no longer supports the
`menuRenderer` and `itemRenderer` props. Instead, there is built-in
support for conditionally rendering as a `Sheet` component using the
`renderAsSheet` prop.

BREAKING CHANGE: The `MenuItemSeparator` now renders as an `<li>`
instead of an `<hr>` or `<div>`.

BREAKING CHANGE: The `DropdownMenu` component now requires a parent
`AppSizeListener` because of the conditional `Sheet` rendering
functionality. This might require updating your tests to either use the
`Configuration` component from `@react-md/layout` (recommended) or
adding the `AppSizeListener` to tests that include `DropdownMenu`s.

BREAKING CHANGE: Menu buttons will no longer open by pressing the
`ArrowUp` or `ArrowDown` keys.

BREAKING CHANGE: Using any of the `MenuItem` components requires the
`<MenuKeyboardFocusProvider>` to be mounted as a parent component which
might affect tests. This will not break anything if you are using the
`DropdownMenu` or `Menu` components.

Author: mlaursen

packages/documentation/src/components/Demos/Form/SelectionControls/MenusWithFormControls.md

@@ -19,9 +19,6 @@ import switchExamples from "./SwitchExamples.md";
 import AsyncSwitchExample from "./AsyncSwitchExample";
 import asyncSwitchExample from "./AsyncSwitchExample.md";
 
-import MenusWithFormControls from "./MenusWithFormControls";
-import menusWithFormControls from "./MenusWithFormControls.md";
-
 const demos: DemoConfig[] = [
   {
     name: "Checkbox and Radio Examples",
@@ -48,11 +45,6 @@ const demos: DemoConfig[] = [
     description: asyncSwitchExample,
     children: <AsyncSwitchExample />,
   },
-  {
-    name: "Menus with Form Controls",
-    description: menusWithFormControls,
-    children: <MenusWithFormControls />,
-  },
 ];
 
 export default function SelectionControls(): ReactElement | null {