Move shared utilities into backend/shared

Clears the root folder of the backend a bit to clarify which parts are entry points.

This follows from these same files being in packages/shared/ since they're
shared by multiple renderers.

packages/react-devtools-extensions/src/contentScripts/renderer.js

@@ -8,7 +8,7 @@
  * @flow
  */
 
-import {attach} from 'react-devtools-shared/src/backend/renderer';
+import {attach} from 'react-devtools-shared/src/backend/fiber/renderer';
 import {SESSION_STORAGE_RELOAD_AND_PROFILE_KEY} from 'react-devtools-shared/src/constants';
 import {sessionStorageGetItem} from 'react-devtools-shared/src/storage';
 

packages/react-devtools-shared/src/backend/console.js

@@ -32,7 +32,7 @@ import {
  supportsOwnerStacks,
  supportsNativeConsoleTasks,
 } from './fiber/DevToolsFiberComponentStack';
-import {formatOwnerStack} from './DevToolsOwnerStack';
+import {formatOwnerStack} from './shared/DevToolsOwnerStack';
 import {castBool, castBrowserTheme} from '../utils';
 
 const OVERRIDE_CONSOLE_METHODS = ['error', 'trace', 'warn'];

packages/react-devtools-shared/src/backend/fiber/DevToolsFiberComponentStack.js

@@ -22,9 +22,9 @@ import {
  describeFunctionComponentFrame,
  describeClassComponentFrame,
  describeDebugInfoFrame,
-} from '../DevToolsComponentStackFrame';
+} from '../shared/DevToolsComponentStackFrame';
 
-import {formatOwnerStack} from '../DevToolsOwnerStack';
+import {formatOwnerStack} from '../shared/DevToolsOwnerStack';
 
 export function describeFiber(
  workTagMap: WorkTagMap,

packages/react-devtools-shared/src/backend/fiber/renderer.js

@@ -95,7 +95,7 @@ import {
  MEMO_NUMBER,
  MEMO_SYMBOL_STRING,
  SERVER_CONTEXT_SYMBOL_STRING,
-} from '../ReactSymbols';
+} from '../shared/ReactSymbols';
 import {enableStyleXFeatures} from 'react-devtools-feature-flags';
 import is from 'shared/objectIs';
 import hasOwnProperty from 'shared/hasOwnProperty';

packages/react-devtools-shared/src/backend/DevToolsComponentStackFrame.js → packages/react-devtools-shared/src/backend/shared/DevToolsComponentStackFrame.js

@@ -12,7 +12,7 @@
 // while still maintaining support for multiple renderer versions
 // (which use different values for ReactTypeOfWork).
 
-import type {CurrentDispatcherRef} from './types';
+import type {CurrentDispatcherRef} from '../types';
 
 // The shared console patching code is DEV-only.
 // We can't use it since DevTools only ships production builds.