Enhance Bilibili video support (redo of #2522) (#2599)

* Enhance support for bilibili videos in responsive video helper, and add corresponding doc

* Apply @iBug's review in mmistakes/minimal-mistakes#2522

* Fix danmaku in page hero video

* Update video to use case..when for iframe src

* Update CHANGELOG and history

Co-authored-by: Anran <51769728+ALeafWolf@users.noreply.github.com>
Co-authored-by: Michael Rose <mmistakes@users.noreply.github.com>

docs/_docs/14-helpers.md

@@ -179,6 +179,7 @@ Embed a video from YouTube, Vimeo, Google Drive, or bilibili that responsively s
 | ---------- | ------------ | ---------------------------------------------------------- |
 | `id`       | **Required** | ID of the video                                            |
 | `provider` | **Required** | Hosting provider of the video: `youtube`, `vimeo`, `google-drive`, or `bilibili` |
+| `danmaku`  | Optional     | Bilibili only, [details below](#Bilibili)                  |
 
 ### YouTube
 
@@ -240,6 +241,30 @@ header:
     provider: google-drive
 ```
 
+### Bilibili
+
+To embed the following Bilibili video at url `https://www.bilibili.com/video/BV1E7411e7hC` into a post or page's main content you'd use:
+
+```liquid
+{% raw %}{% include video id="BV1E7411e7hC" provider="bilibili" %}{% endraw %}
+```
+
+If you want to enable danmaku (弹幕) for the embeded video, which is disabled by default, you can supply an additional parameter `danmaku="1"` as shown below: 
+
+```liquid
+{% raw %}{% include video id="BV1E7411e7hC" provider="bilibili" danmaku="1" %}{% endraw %}
+```
+
+To embed it as a video header you'd use the following YAML Front Matter:
+
+```yaml
+header:
+  video:
+    id: BV1E7411e7hC
+    provider: bilibili
+    danmaku: 1
+```
+
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