Add context when rendering labels or emojis (#23281) (#23319)

Backport #23281

This branch continues the work of #23092 and attempts to rid the
codebase of any `nil` contexts when using a `RenderContext`.

Anything that renders markdown or does post processing may call
`markup.sha1CurrentPatternProcessor()`, and this runs
`git.OpenRepository()`, which needs a context. It will panic if the
context is `nil`. This branch attempts to _always_ include a context
when creating a `RenderContext` to prevent future crashes.

Co-authored-by: Jonathan Tran <jon@allspice.io>

templates/repo/settings/lfs_file_find.tmpl

@@ -19,7 +19,7 @@
 							<td class="message">
 								<span class="truncate">
 									<a href="{{$.RepoLink}}/commit/{{.SHA}}" title="{{.Summary | RenderEmojiPlain}}">
-										{{.Summary | RenderEmoji}}
+										{{.Summary | RenderEmoji $.Context}}
 									</a>
 								</span>
 							</td>