FIX: Video placeholders not auto-linking post uploads (#24559)

Followup to 2443446e62

We introduced video placeholders which prevent preloading
metadata for videos in posts. The structure looks like this
in HTML when the post is cooked:

```
<div class="video-placeholder-container" data-video-src="http://some-url.com/video.mp4" dir="ltr" style="cursor: pointer;">
  <div class="video-placeholder-wrapper">
    <div class="video-placeholder-overlay">
      <svg class="fa d-icon d-icon-play svg-icon svg-string" xmlns="http://www.w3.org/2000/svg">
        <use href="#play"></use>
      </svg>
    </div>
  </div>
</div>
```

However, we did not update the code that links post uploads
to the post via UploadReference, so any videos uploaded since
this change are essentially dangling and liable to be deleted.
This also causes some uploads to be marked secure when they
shouldn't be, because they are not picked up and analysed in the
CookedPostProcessor flow.

app/models/post.rb

@@ -863,7 +863,7 @@ class Post < ActiveRecord::Base
       bypass_bump: bypass_bump,
       cooking_options: self.cooking_options,
       new_post: new_post,
-      post_id: id,
+      post_id: self.id,
       skip_pull_hotlinked_images: skip_pull_hotlinked_images,
     }
 
@@ -1094,7 +1094,15 @@ class Post < ActiveRecord::Base
     ]
 
     fragments ||= Nokogiri::HTML5.fragment(self.cooked)
-    selectors = fragments.css("a/@href", "img/@src", "source/@src", "track/@src", "video/@poster")
+    selectors =
+      fragments.css(
+        "a/@href",
+        "img/@src",
+        "source/@src",
+        "track/@src",
+        "video/@poster",
+        "div/@data-video-src",
+      )
 
     links =
       selectors

spec/models/post_spec.rb

@@ -1628,6 +1628,7 @@ RSpec.describe Post do
 
   describe "uploads" do
     fab!(:video_upload) { Fabricate(:upload, extension: "mp4") }
+    fab!(:video_upload_2) { Fabricate(:upload, extension: "mp4") }
     fab!(:image_upload) { Fabricate(:upload) }
     fab!(:audio_upload) { Fabricate(:upload, extension: "ogg") }
     fab!(:attachment_upload) { Fabricate(:upload, extension: "csv") }
@@ -1636,6 +1637,7 @@ RSpec.describe Post do
 
     let(:base_url) { "#{Discourse.base_url_no_prefix}#{Discourse.base_path}" }
     let(:video_url) { "#{base_url}#{video_upload.url}" }
+    let(:video_2_url) { "#{base_url}#{video_upload_2.url}" }
     let(:audio_url) { "#{base_url}#{audio_upload.url}" }
 
     let(:raw_multiple) { <<~RAW }
@@ -1653,6 +1655,16 @@ RSpec.describe Post do
         <source src="#{audio_url}">
         <a href="#{audio_url}">#{audio_url}</a>
       </audio>
+
+      <div class="video-placeholder-container" data-video-src="#{video_2_url}" dir="ltr" style="cursor: pointer;">
+        <div class="video-placeholder-wrapper">
+          <div class="video-placeholder-overlay">
+            <svg class="fa d-icon d-icon-play svg-icon svg-string" xmlns="http://www.w3.org/2000/svg">
+              <use href="#play"></use>
+            </svg>
+          </div>
+        </div>
+      </div>
       RAW
 
     let(:post) { Fabricate(:post, raw: raw_multiple) }
@@ -1661,7 +1673,7 @@ RSpec.describe Post do
       post.link_post_uploads
 
       post.trash!
-      expect(UploadReference.count).to eq(6)
+      expect(UploadReference.count).to eq(7)
 
       post.destroy!
       expect(UploadReference.count).to eq(0)
@@ -1673,6 +1685,7 @@ RSpec.describe Post do
 
         expect(UploadReference.where(target: post).pluck(:upload_id)).to contain_exactly(
           video_upload.id,
+          video_upload_2.id,
           image_upload.id,
           audio_upload.id,
           attachment_upload.id,
@@ -1901,6 +1914,7 @@ RSpec.describe Post do
       upload5 = Fabricate(:upload)
       upload6 = Fabricate(:video_upload)
       upload7 = Fabricate(:upload, extension: "vtt")
+      upload8 = Fabricate(:video_upload)
 
       set_cdn_url "https://awesome.com/somepath"
 
@@ -1920,6 +1934,16 @@ RSpec.describe Post do
         <source src="#{Discourse.base_url}#{upload6.url}" type="video/mp4" />
         <track src="#{Discourse.base_url}#{upload7.url}" label="English" kind="subtitles" srclang="en" default />
       </video>
+
+      <div class="video-placeholder-container" data-video-src="#{Discourse.base_url}#{upload8.url}" dir="ltr" style="cursor: pointer;">
+        <div class="video-placeholder-wrapper">
+          <div class="video-placeholder-overlay">
+            <svg class="fa d-icon d-icon-play svg-icon svg-string" xmlns="http://www.w3.org/2000/svg">
+              <use href="#play"></use>
+            </svg>
+          </div>
+        </div>
+      </div>
       RAW
 
       urls = []
@@ -1938,6 +1962,7 @@ RSpec.describe Post do
         "#{Discourse.base_url}#{upload5.url}",
         "#{Discourse.base_url}#{upload6.url}",
         "#{Discourse.base_url}#{upload7.url}",
+        "#{Discourse.base_url}#{upload8.url}",
       )
 
       expect(paths).to contain_exactly(
@@ -1948,6 +1973,7 @@ RSpec.describe Post do
         upload5.url,
         upload6.url,
         upload7.url,
+        upload8.url,
       )
     end