Link to previous blames in file blame page (#16259)

Adds a link to each blame hunk, to view the blame of an earlier version of the file, similar to GitHub. Also refactors the blame render from fmtstring based to template based.

* Fix blame bottom line and add blame prior button

* Jump to previous parent commit from the commit.

* Fix previous commit link

* Fix previous blame link

* Fix the given file not exist in the previous commit.

* Fix blameRow struct not export

* fix theming issues, rename template var

* remove unused LastCommit fetch

* fix location of blame-hunk divider

* rewrite previous commit checks

* remove duplicate commit lookup

its already resolved and stored in ctx.Repo.Commit!

* split out blamePart processing into function

Co-authored-by: rogerluo410 <rogerluo410@gmail.com>

web_src/less/themes/theme-arc-green.less

@@ -101,6 +101,7 @@
   --color-markup-code-block: #292d39;
   --color-button: #353846;
   --color-code-bg: #2a2e3a;
+  --color-code-sidebar-bg: #2e323e;
   --color-shadow: #00000060;
   --color-secondary-bg: #2a2e3a;
   --color-text-focus: #fff;
@@ -430,11 +431,6 @@ td.blob-hunk {
   background-color: #bbbbbb !important;
 }
 
-.lines-commit,
-.blame .lines-num {
-  background: #2e323e !important;
-}
-
 .lines-num {
   color: var(--color-secondary-dark-6) !important;
   border-color: var(--color-secondary) !important;