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/commits_list.tmpl

@@ -61,7 +61,7 @@
 						<td class="message">
 							<span class="message-wrapper">
 							{{if $.PageIsWiki}}
-								<span class="commit-summary {{if gt .ParentCount 1}} grey text{{end}}" title="{{.Summary}}">{{.Summary | RenderEmoji}}</span>
+								<span class="commit-summary {{if gt .ParentCount 1}} grey text{{end}}" title="{{.Summary}}">{{.Summary | RenderEmoji $.Context}}</span>
 							{{else}}
 								{{$commitLink:= printf "%s/commit/%s" $commitRepoLink (PathEscape .ID.String)}}
 								<span class="commit-summary {{if gt .ParentCount 1}} grey text{{end}}" title="{{.Summary}}">{{RenderCommitMessageLinkSubject $.Context .Message $commitRepoLink $commitLink $.Repository.ComposeMetas}}</span>