Refactor markup render to fix various path problems (#34114)

* Fix #33972
    * Use consistent path resolving for links and medias.
* No need to make the markup renders to resolve the paths, instead, the
paths are all correctly resolved in the "post process" step.
* Fix #33274
* Since 1.23, all paths starting with "/" are relative to current render
context (for example: the current repo branch)
* Introduce `/:root/path-relative-to-root`, then the path will be
rendered as relative to "ROOT_URL"

modules/markup/html_issue.go

@@ -82,7 +82,7 @@ func createIssueLinkContentWithSummary(ctx *RenderContext, linkHref string, ref
 	h, err := DefaultRenderHelperFuncs.RenderRepoIssueIconTitle(ctx, RenderIssueIconTitleOptions{
 		OwnerName:  ref.Owner,
 		RepoName:   ref.Name,
-		LinkHref:   linkHref,
+		LinkHref:   ctx.RenderHelper.ResolveLink(linkHref, LinkTypeDefault),
 		IssueIndex: issueIndex,
 	})
 	if err != nil {
@@ -162,7 +162,7 @@ func issueIndexPatternProcessor(ctx *RenderContext, node *html.Node) {
 			issueOwner := util.Iif(ref.Owner == "", ctx.RenderOptions.Metas["user"], ref.Owner)
 			issueRepo := util.Iif(ref.Owner == "", ctx.RenderOptions.Metas["repo"], ref.Name)
 			issuePath := util.Iif(ref.IsPull, "pulls", "issues")
-			linkHref := ctx.RenderHelper.ResolveLink(util.URLJoin(issueOwner, issueRepo, issuePath, ref.Issue), LinkTypeApp)
+			linkHref := "/:root/" + util.URLJoin(issueOwner, issueRepo, issuePath, ref.Issue)
 
 			// at the moment, only render the issue index in a full line (or simple line) as icon+title
 			// otherwise it would be too noisy for "take #1 as an example" in a sentence