docs: update NgModule overview for standalone default (angular#58606)

This is the first commit towards updating the NgModule guide to reflect
the fact that v19+ is standalone by default. This PR focuses on:
* Updating the overview to give an actual overview of the most
  important/common uses of `NgModule`
* Add callouts recommending standalone APIs over `NgModule`
* Remove several stale docs that no longer make sense in v19+

This guide (directory) needs additional follow up work; I plan to
address the remaining content in follow-up changes.

PR Close angular#58606

Author: jelbourn

adev/src/app/sub-navigation-data.ts

@@ -1457,36 +1457,6 @@ const REFERENCE_SUB_NAVIGATION_DATA: NavigationItem[] = [
             path: 'guide/ngmodules',
             contentPath: 'guide/ngmodules/overview',
           },
-          {
-            label: 'JS Modules vs NgModules',
-            path: 'guide/ngmodules/vs-jsmodule',
-            contentPath: 'guide/ngmodules/vs-jsmodule',
-          },
-          {
-            label: 'Launching your app with a root module',
-            path: 'guide/ngmodules/bootstrapping',
-            contentPath: 'guide/ngmodules/bootstrapping',
-          },
-          {
-            label: 'Sharing NgModules',
-            path: 'guide/ngmodules/sharing',
-            contentPath: 'guide/ngmodules/sharing',
-          },
-          {
-            label: 'Frequently used NgModules',
-            path: 'guide/ngmodules/frequent',
-            contentPath: 'guide/ngmodules/frequent',
-          },
-          {
-            label: 'Feature modules',
-            path: 'guide/ngmodules/feature-modules',
-            contentPath: 'guide/ngmodules/feature-modules',
-          },
-          {
-            label: 'Types of feature modules',
-            path: 'guide/ngmodules/module-types',
-            contentPath: 'guide/ngmodules/module-types',
-          },
           {
             label: 'Providing dependencies',
             path: 'guide/ngmodules/providers',
@@ -1502,11 +1472,6 @@ const REFERENCE_SUB_NAVIGATION_DATA: NavigationItem[] = [
             path: 'guide/ngmodules/lazy-loading',
             contentPath: 'guide/ngmodules/lazy-loading',
           },
-          {
-            label: 'NgModule API',
-            path: 'guide/ngmodules/api',
-            contentPath: 'guide/ngmodules/api',
-          },
           {
             label: 'NgModule FAQs',
             path: 'guide/ngmodules/faq',

adev/src/content/guide/ngmodules/api.md

@@ -13,7 +13,7 @@ Declare them in a module if they belong to that particular module.
 
 ## What is a `declarable`?
 
-Declarables are the class types —components, directives, and pipes— that you can add to a module's `declarations` list.
+Declarables are the class types— components, directives, and pipes— that you can add to a module's `declarations` list.
 They're the only classes that you can add to `declarations`.
 
 ## What classes should I *not* add to `declarations`?