js: reorganize Javascript file structure.

Move Javascript files from app/components/**/*.js back to app/javascript/src/javascripts/*.js.
This way Javascript files are in one place, which simplifies import paths and makes it
easier to see all Javascript at once.

app/javascript/src/javascripts/forum_post_component.js

@@ -0,0 +1,48 @@
+import Utility from "./utility";
+
+class ForumPostComponent {
+  static initialize() {
+    if ($("#c-forum-topics #a-show, #c-forum-posts #a-show").length) {
+      $(document).on("click.danbooru.forum_post", ".edit_forum_post_link", ForumPostComponent.showEditPostForm);
+      $(document).on("click.danbooru.forum_post", ".edit_forum_topic_link", ForumPostComponent.showEditTopicForm);
+      $(document).on("click.danbooru.forum_post", "#new-response-link", ForumPostComponent.showNewForumPostForm);
+      $(document).on("click.danbooru.forum_post", ".forum-post-copy-id", ForumPostComponent.copyID);
+      $(document).on("click.danbooru.forum_post", ".forum-post-copy-link", ForumPostComponent.copyLink);
+    }
+  }
+
+  static showNewForumPostForm(e) {
+    $("#topic-response").show();
+    $("#forum_post_body").get(0).scrollIntoView(false);
+    $("#forum_post_body").selectEnd();
+    e.preventDefault();
+  }
+
+  static showEditPostForm(e) {
+    $(this).closest(".forum-post").find(".edit_forum_post").show();
+    e.preventDefault();
+  }
+
+  static showEditTopicForm(e) {
+    $(this).closest(".forum-post").find(".edit_forum_topic").show();
+    e.preventDefault();
+  }
+
+  static async copyID(e) {
+    let id = $(this).closest(".forum-post").data("id");
+    let link = `forum #${id}`;
+    Utility.copyToClipboard(link);
+    e.preventDefault();
+  }
+
+  static async copyLink(e) {
+    let id = $(this).closest(".forum-post").data("id");
+    let link = `${window.location.origin}/forum_posts/${id}`;
+    Utility.copyToClipboard(link);
+    e.preventDefault();
+  }
+}
+
+$(document).ready(ForumPostComponent.initialize);
+
+export default ForumPostComponent;