onboarding: Add highlighted-element class to <b> in onboarding modals.

This commit adds 'highlighted-element' class to <b> tags in
the following onboarding modals:
* introduce inbox view modal
* introduce recent conversations view modal
* introduce resolve topic modal
* introduce first channel created modal

'highlighted-element' class sets the 'font-weight: 600',
replacing the default of 700.

web/templates/confirm_dialog/intro_resolve_topic.hbs

@@ -1,5 +1,6 @@
 {{#tr}}
-You're marking the topic <b>{topic_name}</b> as resolved. This adds a ✔ at the beginning of the topic name to let everyone know that this conversation is done. <z-link>Learn more</z-link>
+You're marking the topic <z-highlight>{topic_name}</z-highlight> as resolved. This adds a ✔ at the beginning of the topic name to let everyone know that this conversation is done. <z-link>Learn more</z-link>
 {{#*inline "z-link"}}<a target="_blank" rel="noopener noreferrer" href="/help/resolve-a-topic">{{>
     @partial-block}}</a>{{/inline}}
+{{#*inline "z-highlight"}}<b class="highlighted-element">{{> @partial-block}}</b>{{/inline}}
 {{/tr}}

web/templates/introduce_zulip_view_modal.hbs

@@ -1,26 +1,43 @@
 <div id="introduce-zulip-view-modal">
     <p>
         {{#if (eq zulip_view "inbox")}}
-            {{#tr}}You’ll see a list of <b>conversations</b> where you have <b>unread messages</b>, organized by channel.{{/tr}}
+            {{#tr}}
+                You’ll see a list of <z-highlight>conversations</z-highlight> where you have <z-highlight>unread messages</z-highlight>, organized by channel.
+                {{#*inline "z-highlight"}}<b class="highlighted-element">{{> @partial-block}}</b>{{/inline}}
+            {{/tr}}
         {{else if (eq zulip_view "recent_conversations")}}
-            {{#tr}}You’ll see a list of <b>ongoing conversations</b>.{{/tr}}
+            {{#tr}}
+                You’ll see a list of <z-highlight>ongoing conversations</z-highlight>.
+                {{#*inline "z-highlight"}}<b class="highlighted-element">{{> @partial-block}}</b>{{/inline}}
+            {{/tr}}
         {{/if}}
-        {{#tr}}Each conversation is <b>labeled with a topic</b> by the person who started it.{{/tr}}
+
+        {{#tr}}
+            Each conversation is <z-highlight>labeled with a topic</z-highlight> by the person who started it.
+            {{#*inline "z-highlight"}}<b class="highlighted-element">{{> @partial-block}}</b>{{/inline}}
+        {{/tr}}
     </p>
     <p>
         {{t 'Click on a conversation to view it. To return here, you can:'}}
         <ul>
-            <li>{{#tr}}Use the <b>back</b> button in your browser or desktop app.{{/tr}}</li>
+            <li>
+                {{#tr}}
+                    Use the <z-highlight>back</z-highlight> button in your browser or desktop app.
+                    {{#*inline "z-highlight"}}<b class="highlighted-element">{{> @partial-block}}</b>{{/inline}}
+                {{/tr}}
+            </li>
             <li>
                 {{#if (eq zulip_view "inbox")}}
                     {{#tr}}
-                        Click <z-icon-inbox></z-icon-inbox> <b>Inbox</b> in the left sidebar.
+                        Click <z-icon-inbox></z-icon-inbox> <z-highlight>Inbox</z-highlight> in the left sidebar.
                         {{#*inline "z-icon-inbox"}}<i class="zulip-icon zulip-icon-inbox" aria-hidden="true"></i>{{/inline}}
+                        {{#*inline "z-highlight"}}<b class="highlighted-element">{{> @partial-block}}</b>{{/inline}}
                     {{/tr}}
                 {{else if (eq zulip_view "recent_conversations")}}
                     {{#tr}}
-                        Click <z-icon-recent></z-icon-recent> <b>Recent conversations</b> in the left sidebar.
+                        Click <z-icon-recent></z-icon-recent> <z-highlight>Recent conversations</z-highlight> in the left sidebar.
                         {{#*inline "z-icon-recent"}}<i class="zulip-icon zulip-icon-recent" aria-hidden="true"></i>{{/inline}}
+                        {{#*inline "z-highlight"}}<b class="highlighted-element">{{> @partial-block}}</b>{{/inline}}
                     {{/tr}}
                 {{/if}}
             </li>

web/templates/stream_settings/first_stream_created_modal.hbs

@@ -3,12 +3,13 @@
     <li>
         {{#tr}}
         Click on <z-stream></z-stream> at the top of your Zulip window.
-        {{#*inline "z-stream"}}<b>{{> ../inline_decorated_channel_name stream=stream}}</b>{{/inline}}
+        {{#*inline "z-stream"}}<b class="highlighted-element">{{> ../inline_decorated_channel_name stream=stream}}</b>{{/inline}}
         {{/tr}}
     </li>
     <li>
         {{#tr}}
-        Use the <b>back</b> button in your browser or desktop app.
+        Use the <z-highlight>back</z-highlight> button in your browser or desktop app.
+        {{#*inline "z-highlight"}}<b class="highlighted-element">{{> @partial-block}}</b>{{/inline}}
         {{/tr}}
     </li>
 </ul>