[drilldown] fix Darktheme is missing from add drilldowns panel (#147270)

Fixes https://github.com/elastic/kibana/issues/147147

Replaces https://github.com/elastic/kibana/pull/147151. Thanks for the
tip @Dosant

PR passes theme$ to toMountPoint

<img width="400" alt="Screen Shot 2022-12-06 at 4 54 49 PM"
src="https://user-images.githubusercontent.com/373691/206051509-207c39f6-125d-46f9-baab-87a5a96a6541.png">

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

x-pack/plugins/dashboard_enhanced/public/services/drilldowns/actions/flyout_create_drilldown/flyout_create_drilldown.test.tsx

@@ -26,6 +26,9 @@ const actionParams: OpenFlyoutAddDrilldownParams = {
       application: {
         currentAppId$: new Subject(),
       },
+      theme: {
+        theme$: new Subject(),
+      },
     } as any,
     plugins: {
       uiActionsEnhanced,

x-pack/plugins/dashboard_enhanced/public/services/drilldowns/actions/flyout_create_drilldown/flyout_create_drilldown.tsx

@@ -106,7 +106,8 @@ export class FlyoutCreateDrilldownAction implements Action<EmbeddableContext> {
           placeContext={{ embeddable }}
           templates={templates}
           onClose={close}
-        />
+        />,
+        { theme$: core.theme.theme$ }
       ),
       {
         ownFocus: true,

x-pack/plugins/dashboard_enhanced/public/services/drilldowns/actions/flyout_edit_drilldown/flyout_edit_drilldown.test.tsx

@@ -36,6 +36,9 @@ const actionParams: FlyoutEditDrilldownParams = {
       application: {
         currentAppId$: new Subject(),
       },
+      theme: {
+        theme$: new Subject(),
+      },
     } as any,
     plugins: {
       uiActionsEnhanced: uiActions,

x-pack/plugins/dashboard_enhanced/public/services/drilldowns/actions/flyout_edit_drilldown/flyout_edit_drilldown.tsx

@@ -80,7 +80,8 @@ export class FlyoutEditDrilldownAction implements Action<EmbeddableContext> {
           placeContext={{ embeddable }}
           templates={templates}
           onClose={close}
-        />
+        />,
+        { theme$: core.theme.theme$ }
       ),
       {
         ownFocus: true,