Add copy link and highlight to comments

Opening a comment link expands the revision the comment is in, even if
the link is opened while already on the page, and scrolls to it.

This also fixes scrolling to URL fragments that aren't valid CSS
selectors, such as comment ids starting with a digit.

src/views/repos/Cob/Revision.svelte

@@ -13,7 +13,7 @@
   import * as utils from "@app/lib/utils";
   import { HttpdClient } from "@http-client";
   import { cachedGetDiff } from "@app/views/repos/router";
-  import { onMount } from "svelte";
+  import { onMount, tick } from "svelte";
 
   import CobCommitTeaser from "@app/views/repos/Cob/CobCommitTeaser.svelte";
   import CommentComponent from "@app/components/Comment.svelte";
@@ -55,7 +55,41 @@
   export let previousRevOid: string | undefined = undefined;
   export let first: boolean;
 
-  let expanded = initiallyExpanded;
+  function timelinesContain(commentId: string | undefined): boolean {
+    if (commentId === undefined) {
+      return false;
+    }
+    const inThread = (thread: { root: Comment; replies: Comment[] }) =>
+      thread.root.id === commentId ||
+      thread.replies.some(reply => reply.id === commentId);
+    return timelines.some(element => {
+      switch (element.type) {
+        case "thread":
+          return inThread(element.inner);
+        case "review": {
+          const review = element.inner[1];
+          return review.id === commentId || review.threads.some(inThread);
+        }
+        case "merge":
+          return false;
+      }
+    });
+  }
+
+  let expanded =
+    initiallyExpanded ||
+    timelinesContain(utils.fragmentId(window.location.hash));
+
+  async function expandToHash() {
+    const commentId = utils.fragmentId(window.location.hash);
+    if (expanded || commentId === undefined || !timelinesContain(commentId)) {
+      return;
+    }
+    expanded = true;
+    await tick();
+    utils.scrollIntoView(commentId);
+  }
+
   const api = new HttpdClient(baseUrl);
   const lastEdit = revisionEdits.at(-1);
 
@@ -273,6 +307,8 @@
   }
 </style>
 
+<svelte:window on:hashchange={expandToHash} />
+
 <div class="revision" style:margin-bottom={expanded ? "2rem" : "0.5rem"}>
   <div class="revision-box" class:expanded>
     <div class="revision-header">