change some references back to register, and update a few docs

docs/snippets/common/my-addon-preset-implementation.js.mdx

@@ -2,7 +2,7 @@
 // /my-addon/src/preset.js
 
 function managerEntries(entry = []) {
-  return [...entry, require.resolve("./manager")]; //👈 Addon implementation
+  return [...entry, require.resolve("./register")]; //👈 Addon implementation
 }
 
 module.exports = { managerEntries }

docs/snippets/common/storybook-addon-load-external-addons-preset.js.mdx

@@ -2,7 +2,7 @@
 // my-preset/index.js
 
 function managerEntries(entry = []) {
-  return [...entry, require.resolve('my-other-addon/manager')];
+  return [...entry, require.resolve('my-other-addon/register')];
 }
 
 const config = (entry = [], options) => {

docs/snippets/common/storybook-addon-preset-example.js.mdx

@@ -6,7 +6,7 @@ export function config(entry = []) {
 }
 
 export function managerEntries(entries) {
-  return [...entries, require.resolve('./manager')];
+  return [...entries, require.resolve('./register')];
 }
 
 export const parameters = {

docs/snippets/common/storybook-main-register-presets-managerentry.js.mdx

@@ -3,7 +3,6 @@
 
 module.exports = {
   addons: [
-    '@storybook/addon-storysource/manager', // A managerEntry registered here, in this case from the storysource addon.
     '@storybook/addon-docs/preset', // A preset registered here, in this case from the addon-docs addon.
   ],
 };

docs/snippets/common/storybook-main-use-manager-entries.js.mdx

@@ -2,6 +2,6 @@
 // .storybook/main.js
 
 module.exports = {
-  managerEntries: ['@storybook/addon-storysource/manager'],
+  managerEntries: ['some-storybook-addon/entry-point.js'],
 };
 ```

docs/snippets/common/storybook-storysource-manager-entries.js.mdx

@@ -1,7 +1,5 @@
 ```js
 // storysource/preset.js
 
-export function managerEntries(entry = []) {
-  return [...entry, require.resolve('@storybook/addon-storysource/manager')];
-}
+/* nothing needed */
 ```

lib/core-common/src/presets.ts

@@ -106,13 +106,20 @@ export const resolveAddonName = (
   }
 
   if (managerFile || registerFile || previewFile || presetFile) {
+    const managerEntries = [];
+
+    if (managerFile) {
+      managerEntries.push(managerFile);
+    }
+    // register file is the old way of registering addons
+    if (!managerFile && registerFile && !presetFile) {
+      managerEntries.push(registerFile);
+    }
+
     return {
       type: 'virtual',
       name: path,
-      // register file is the old way of registering addons
-      ...(managerFile || registerFile
-        ? { managerEntries: [managerFile, !presetFile && registerFile].filter(Boolean) }
-        : {}),
+      ...(managerEntries.length ? { managerEntries } : {}),
       ...(previewFile ? { previewAnnotations: [previewFile] } : {}),
       ...(presetFile ? { presets: [{ name: presetFile, options }] } : {}),
     };