feat(keyboard-keys): Export keys and legacy keyCodes

This PR implements what was proposed in microsoft#18587 and exports all named
`key` values specified by w3c.

Also adds legacy keycode exports as a deep import. Happy to take any
suggestions to avoid this. Originallly this was the plan:

```ts
export * as keyCodes from './keyCodes'
```

but unfortunately API extractor does not support this syntax
microsoft/rushstack#2780

packages/keyboard-keys/README.md

@@ -1,3 +1,45 @@
 # @fluentui/keyboard-keys
 
-Contains a set of keyboard constants for key and keyCode comparison in components
+Contains a set of keyboard constants for key and keyCode comparison in components. This package contains
+**named key values** from [The w3 uievents-key specification](https://www.w3.org/TR/uievents-key/).
+
+Unicode values are not included since there are a lot of locales to consider and they provide no benefit since
+unicode characters can be used directly in code.
+
+# Usage
+
+```ts
+import { Enter } from '@fluentui/keyboard-keys';
+
+const onKeyDown = (e: React.KeyboardEvent) => {
+  if (e.key === Enter) {
+    // ...
+  }
+
+  // Unicode characters 'a', '1', '%'...
+  // should be used directly in code
+  if (e.key === 'a') {
+    // ...
+  }
+};
+```
+
+## Legacy keyCode
+
+In order to migrate easily from `@fluentui/keyboard-key` legacy `keyCode` support is available in this library but
+is not encouraged for reuse since this propoerty has been deprecated for a while and will be removed in future
+standards.
+
+```ts
+import { Enter, a } from '@fluentui/keyboard-keys/lib/keyCodes';
+
+const onKeyDown = (e: React.KeyboardEvent) => {
+  if (e.keyCode === Enter) {
+    // ...
+  }
+
+  if (e.key === a) {
+    // ...
+  }
+};
+```

packages/keyboard-keys/bundle-size/MultipleKeyCodes.fixture.js

@@ -0,0 +1,7 @@
+import { Enter, Tab, ArrowDown, ArrowLeft, ArrowRight } from '@fluentui/keyboard-keys/lib/keyCodes';
+
+console.log(Enter, Tab, ArrowDown, ArrowLeft, ArrowRight);
+
+export default {
+  name: 'Multiple keyCodes',
+};

packages/keyboard-keys/bundle-size/MultipleKeys.fixture.js

@@ -0,0 +1,7 @@
+import { Enter, Tab, ArrowDown, ArrowLeft, ArrowRight } from '@fluentui/keyboard-keys';
+
+console.log(Enter, Tab, ArrowDown, ArrowLeft, ArrowRight);
+
+export default {
+  name: 'Multiple keys',
+};

packages/keyboard-keys/bundle-size/SingleKey.fixture.js

@@ -0,0 +1,7 @@
+import { Enter } from '@fluentui/keyboard-keys';
+
+console.log(Enter);
+
+export default {
+  name: 'Single key',
+};

packages/keyboard-keys/bundle-size/SingleKeyCode.fixture.js

@@ -0,0 +1,7 @@
+import { Enter } from '@fluentui/keyboard-keys/lib/keyCodes';
+
+console.log(Enter);
+
+export default {
+  name: 'Single keyCode',
+};