Dashboard import: Bug fixes (#23591)

* clear dashboard on unmount

* fix menu z-index, folderpicker width

* fix issue with saving dashboard in another folder

* use foldermodel instead of selectablevalue

* using z-index from theme

* updated names

* update snapshot

* remove size from folderpicker

* use connectWithCleanup

* update snapshot

packages/grafana-ui/src/components/Select/SelectBase.tsx

@@ -332,6 +332,8 @@ export function SelectBase<T>({
           }),
           container: () => ({
             position: 'relative',
+            // This puts the menu above Inputs (z-index: 1)
+            zIndex: theme.zIndex.dropdown,
             width: width ? `${8 * width}px` : '100%',
           }),
         }}