Frontend: Add a first page and previous page buttons for channel navigation (#4123)

src/invidious/views/channel.ecr

@@ -20,7 +20,9 @@
 
   page_nav_html = IV::Frontend::Pagination.nav_ctoken(locale,
     base_url: relative_url,
-    ctoken: next_continuation
+    ctoken: next_continuation,
+    first_page: continuation.nil?,
+    params: env.params.query,
   )
 %>
 
@@ -40,6 +42,8 @@
 <link rel="alternate" type="application/rss+xml" title="RSS" href="/feed/channel/<%= ucid %>" />
 <%- end -%>
 
+<script src="/js/pagination.js?v=<%= ASSET_COMMIT %>"></script>
+
 <link rel="alternate" href="<%= youtube_url %>">
 <title><%= author %> - Invidious</title>
 <% end %>

src/invidious/views/components/items_paginated.ecr

@@ -8,4 +8,14 @@
 
 <%= page_nav_html %>
 
+<script id="pagination-data" type="application/json">
+<%=
+{
+   "next_page" => translate(locale, "Next page"),
+   "prev_page" => translate(locale, "Previous page"),
+   "is_rtl"    => locale_is_rtl?(locale)
+}.to_pretty_json
+%>
+</script>
+
 <script src="/js/watched_indicator.js"></script>