Yarn workspaces

Summary:
1) moved "sonar/desktop/src" to "sonar/desktop/app/src", so "app" is now a separate package containing the core Flipper app code
2) Configured yarn workspaces with the root in "sonar/desktop": app, static, pkg, doctor, headless-tests. Plugins are not included for now, I plan to do this later.

Reviewed By: jknoxville

Differential Revision: D20535782

fbshipit-source-id: 600b2301960f37c7d72166e0d04eba462bec9fc1

desktop/app/src/ui/components/ErrorBlock.tsx

@@ -0,0 +1,48 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import styled from '@emotion/styled';
+import React from 'react';
+import CodeBlock from './CodeBlock';
+
+export const ErrorBlockContainer = styled(CodeBlock)({
+  backgroundColor: '#f2dede',
+  border: '1px solid #ebccd1',
+  borderRadius: 4,
+  color: '#a94442',
+  overflow: 'auto',
+  padding: 10,
+  whiteSpace: 'pre',
+});
+ErrorBlockContainer.displayName = 'ErrorBlock:ErrorBlockContainer';
+
+/**
+ * Displaying error messages in a red box.
+ */
+export default class ErrorBlock extends React.Component<{
+  /** Error message to display. Error object's `stack` or `message` property is used. */
+  error: Error | string | null;
+  /** Additional className added to the container. */
+  className?: string;
+}> {
+  render() {
+    const {className, error} = this.props;
+
+    let stack = 'Unknown Error';
+    if (typeof error === 'string') {
+      stack = error;
+    } else if (error && typeof error === 'object') {
+      stack = error.stack || error.message || stack;
+    }
+
+    return (
+      <ErrorBlockContainer className={className}>{stack}</ErrorBlockContainer>
+    );
+  }
+}