Upgrade Fluent UI v8 (#688)

Co-authored-by: Steve Faulkner <southpolesteve@gmail.com>

src/Explorer/Controls/FeaturePanel/FeaturePanelComponent.tsx

@@ -1,9 +1,14 @@
+import {
+  Checkbox,
+  DefaultButton,
+  Dropdown,
+  IDropdownOption,
+  IDropdownStyles,
+  ITextFieldStyles,
+  Stack,
+  TextField,
+} from "@fluentui/react";
 import * as React from "react";
-import { Stack } from "office-ui-fabric-react/lib/Stack";
-import { Dropdown, IDropdownOption, IDropdownStyles } from "office-ui-fabric-react/lib/Dropdown";
-import { Checkbox } from "office-ui-fabric-react/lib/Checkbox";
-import { TextField, ITextFieldStyles } from "office-ui-fabric-react/lib/TextField";
-import { DefaultButton } from "office-ui-fabric-react";
 import "./FeaturePanelComponent.less";
 
 export const FeaturePanelComponent: React.FunctionComponent = () => {

src/Explorer/Controls/FeaturePanel/FeaturePanelLauncher.tsx

@@ -1,6 +1,6 @@
 import * as React from "react";
 import { FeaturePanelComponent } from "./FeaturePanelComponent";
-import { getTheme, mergeStyleSets, FontWeights, Modal, IconButton, IIconProps } from "office-ui-fabric-react";
+import { getTheme, mergeStyleSets, FontWeights, Modal, IconButton, IIconProps } from "@fluentui/react";
 import "./FeaturePanelLauncher.less";
 
 // Modal wrapper

src/Explorer/Controls/FeaturePanel/__snapshots__/FeaturePanelComponent.test.tsx.snap

@@ -57,7 +57,7 @@ exports[`Feature panel renders all flags 1`] = `
         }
       }
     >
-      <StyledWithResponsiveMode
+      <Dropdown
         label="Base Url"
         onChange={[Function]}
         options={
@@ -85,7 +85,7 @@ exports[`Feature panel renders all flags 1`] = `
           }
         }
       />
-      <StyledWithResponsiveMode
+      <Dropdown
         label="Platform"
         onChange={[Function]}
         options={