grafana/ui: Rename Flex component to Stack (#77453)

* grafana/ui: Remove Stack and rename FLex to Stack

* Update types

* Update grafana/ui imports

* Update Grafana imports

* Update docs

public/app/core/components/AppChrome/DockedMegaMenu/MegaMenu.tsx

@@ -6,7 +6,7 @@ import { useLocation } from 'react-router-dom';
 import { GrafanaTheme2 } from '@grafana/data';
 import { selectors } from '@grafana/e2e-selectors';
 import { CustomScrollbar, Icon, IconButton, useStyles2 } from '@grafana/ui';
-import { Flex } from '@grafana/ui/src/unstable';
+import { Stack } from '@grafana/ui/src/unstable';
 import { useGrafana } from 'app/core/context/GrafanaContext';
 import { t } from 'app/core/internationalization';
 import { useSelector } from 'app/types';
@@ -55,7 +55,7 @@ export const MegaMenu = React.memo(
           <CustomScrollbar showScrollIndicators hideHorizontalTrack>
             <ul className={styles.itemList}>
               {navItems.map((link, index) => (
-                <Flex key={link.text} direction="row" alignItems="center">
+                <Stack key={link.text} direction="row" alignItems="center">
                   <MegaMenuItem
                     link={link}
                     onClick={state.megaMenu === 'open' ? onClose : undefined}
@@ -74,7 +74,7 @@ export const MegaMenu = React.memo(
                       variant="secondary"
                     />
                   )}
-                </Flex>
+                </Stack>
               ))}
             </ul>
           </CustomScrollbar>