Fixes dropdown snippets (#25301)

* Make dropright snippet the same as demo

* Add missing .dropdown-toggle-split class

* Make clear the split button label the same as demo

docs/4.0/components/dropdowns.md

@@ -317,7 +317,7 @@ Button dropdowns work with buttons of all sizes, including default and split dro
 </div>
 <div class="btn-group">
   <button class="btn btn-secondary btn-lg" type="button">
-    Large button
+    Large split button
   </button>
   <button type="button" class="btn btn-lg btn-secondary dropdown-toggle dropdown-toggle-split" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
     <span class="sr-only">Toggle Dropdown</span>
@@ -338,7 +338,7 @@ Button dropdowns work with buttons of all sizes, including default and split dro
 </div>
 <div class="btn-group">
   <button class="btn btn-secondary btn-sm" type="button">
-    Small button
+    Small split button
   </button>
   <button type="button" class="btn btn-sm btn-secondary dropdown-toggle dropdown-toggle-split" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
     <span class="sr-only">Toggle Dropdown</span>
@@ -400,7 +400,7 @@ Trigger dropdown menus above elements by adding `.dropup` to the parent element.
   <button type="button" class="btn btn-secondary">
     Split dropup
   </button>
-  <button type="button" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
+  <button type="button" class="btn btn-secondary dropdown-toggle dropdown-toggle-split" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
     <span class="sr-only">Toggle Dropdown</span>
   </button>
   <div class="dropdown-menu">
@@ -447,9 +447,8 @@ Trigger dropdown menus at the right of the elements by adding `.dropright` to th
 {% highlight html %}
 <!-- Default dropright button -->
 <div class="btn-group dropright">
-  <button type="button" class="btn btn-secondary">Dropright</button>
   <button type="button" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
-    <span class="sr-only">Toggle Dropright</span>
+    Dropright
   </button>
   <div class="dropdown-menu">
     <!-- Dropdown menu links -->
@@ -461,7 +460,7 @@ Trigger dropdown menus at the right of the elements by adding `.dropright` to th
   <button type="button" class="btn btn-secondary">
     Split dropright
   </button>
-  <button type="button" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
+  <button type="button" class="btn btn-secondary dropdown-toggle dropdown-toggle-split" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
     <span class="sr-only">Toggle Dropright</span>
   </button>
   <div class="dropdown-menu">