Fix code highlighting on blame page (#36157)

1. Full file highlighting (fix the legacy todo "we should instead
highlight the whole file at once")
    * Fix #24383
2. Correctly covert file content encoding
3. Remove dead code, split large for-loop into small functions/blocks to
make code maintainable

web_src/css/base.css

@@ -919,7 +919,7 @@ overflow-menu .ui.label {
 .blame-avatar {
   display: flex;
   align-items: center;
-  margin-right: 4px;
+  margin-right: 6px;
 }
 
 tr.top-line-blame {