Reduce repaints on blame page

Reduces the repaints on the blame page by setting:
content-visibility: auto

Changelog: performance

app/assets/stylesheets/framework/files.scss

@@ -136,6 +136,13 @@
      *  Blame file
      */
     &.blame {
+      //
+      // IMPORTANT PERFORMANCE OPTIMIZATION
+      //
+      // When viewinng a blame with many commits a lot of content is rendered on the page.
+      // The line below ensures that we only render what is visible to the user, thus reducing TBT in the browser.
+      content-visibility: auto;
+
       table {
         border: 0;
         margin: 0;
@@ -150,6 +157,12 @@
       }
 
       td {
+        //
+        // IMPORTANT PERFORMANCE OPTIMIZATION
+        //
+        // When viewinng a blame with many commits a lot of content is rendered on the page.
+        // The line below ensures that we only render what is visible to the user, thus reducing TBT in the browser.
+        content-visibility: auto;
         border-top: 0;
         border-bottom: 0;
 

app/views/projects/blame/show.html.haml

@@ -51,7 +51,7 @@
                     = i
                 \
 
-            %td.lines
+            %td.lines.gl-w-full
               %pre.code.highlight
                 %code
                   - blame_group[:lines].each do |line|