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>

modules/markup/html.go

@@ -291,9 +291,10 @@ func RenderDescriptionHTML(
 // RenderEmoji for when we want to just process emoji and shortcodes
 // in various places it isn't already run through the normal markdown processor
 func RenderEmoji(
+	ctx *RenderContext,
 	content string,
 ) (string, error) {
-	return renderProcessString(&RenderContext{}, emojiProcessors, content)
+	return renderProcessString(ctx, emojiProcessors, content)
 }
 
 var (