help: Document "Start new conversation" button.

- Documents the new contextually-aware button since the instructions
  now differ depending on whether you're currently in a direct message
  view or not.
- Simplifies the new topic instructions by combining the first two
  tabs into a single web/desktop tab, with an optional step 2 to
  change the destination stream.

Fixes #27159.

help/direct-messages.md

@@ -19,14 +19,19 @@ and do not appear in your list of streams.
 
 {tab|desktop-web}
 
-1. Click the **New direct message** button at the bottom of the app, or
-   use the <kbd>X</kbd> keyboard shortcut.
+1. Click the **New direct message** button at the bottom of the app, or the
+   **Start new conversation** button if you are in a direct message view.
 
 1. Start typing the name of the person you want to message, and
    select their name from the list of suggestions.
 
 {!compose-and-send-message.md!}
 
+!!! keyboard_tip ""
+
+    You can also use the <kbd>X</kbd> keyboard shortcut to start a new direct
+    message conversation.
+
 !!! tip ""
 
       You can also click on any user in the right sidebar to start composing

help/include/how-to-start-a-new-topic.md

@@ -1,10 +1,14 @@
 {start_tabs}
 
-{tab|stream}
+{tab|desktop-web}
 
-1. Click the **New topic** button at the bottom of the app, or
+1. Click the **Start new conversation** button at the bottom of the app, or
    use the <kbd>C</kbd> keyboard shortcut.
 
+1. _(optional)_ You can change the destination stream for your message using
+   the dropdown in the top left of the compose box. You can start typing to
+   filter streams.
+
 1. Enter a topic name. Auto-complete will provide suggestions for previously
    used topics.
 
@@ -12,27 +16,9 @@
 
 !!! tip ""
 
-    You can change the destination stream for your message using the dropdown
-    in the top left of the compose box.
-
-!!! warn ""
-
-    In Zulip, you can compose a message to a different place than the one you
-    are viewing. In this situation, the message feed will fade to indicate
-    what's going on.
-
-{tab|not-stream}
-
-1. Click the **New topic** button at the bottom of the app, or
-   use the <kbd>C</kbd> keyboard shortcut.
-
-1. Select a stream from the dropdown in the top left of the compose box. You can
-   start typing to filter streams.
-
-1. Enter a topic name. Auto-complete will provide suggestions for previously
-   used topics.
-
-{!compose-and-send-message.md!}
+    You can click on the
+    **Clear topic** (<i class="zulip-icon zulip-icon-close"></i>) icon
+    near the upper right of the compose box to erase the topic name.
 
 !!! warn ""
 

help/include/send-group-dm.md

@@ -2,8 +2,8 @@
 
 {tab|desktop-web}
 
-1. Click the **New direct message** button at the bottom of the app, or
-   use the <kbd>X</kbd> keyboard shortcut.
+1. Click the **New direct message** button at the bottom of the app, or the
+   **Start new conversation** button if you are in a direct message view.
 
 1. Start typing the name of the person you want to message, and
    select their name from the list of suggestions. You can continue
@@ -11,6 +11,11 @@
 
 {!compose-and-send-message.md!}
 
+!!! keyboard_tip ""
+
+    You can also use the <kbd>X</kbd> keyboard shortcut to start a new direct
+    message conversation.
+
 !!! tip ""
 
     You can switch from composing a stream message to composing a direct

help/open-the-compose-box.md

@@ -7,7 +7,7 @@ space for the message feed. There are a number of ways to open the compose box.
 
 * Click on any message.
 
-* Click on **Message...**, **New topic**, or **New direct message** at the
+* Click on **Start new conversation**, or **New direct message** at the
   bottom of the app.
 
 ## Using the keyboard