Refactor markup render system (#32612)

This PR removes (almost) all path tricks, and introduces "renderhelper"
package.

Now we can clearly see the rendering behaviors for comment/file/wiki,
more details are in "renderhelper" tests.

Fix #31411 , fix #18592, fix #25632 and maybe more problems. (ps: fix
#32608 by the way)

models/renderhelper/commit_checker.go

@@ -0,0 +1,53 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package renderhelper
+
+import (
+	"context"
+	"io"
+
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/gitrepo"
+	"code.gitea.io/gitea/modules/log"
+)
+
+type commitChecker struct {
+	ctx           context.Context
+	commitCache   map[string]bool
+	gitRepoFacade gitrepo.Repository
+
+	gitRepo       *git.Repository
+	gitRepoCloser io.Closer
+}
+
+func newCommitChecker(ctx context.Context, gitRepo gitrepo.Repository) *commitChecker {
+	return &commitChecker{ctx: ctx, commitCache: make(map[string]bool), gitRepoFacade: gitRepo}
+}
+
+func (c *commitChecker) Close() error {
+	if c != nil && c.gitRepoCloser != nil {
+		return c.gitRepoCloser.Close()
+	}
+	return nil
+}
+
+func (c *commitChecker) IsCommitIDExisting(commitID string) bool {
+	exist, inCache := c.commitCache[commitID]
+	if inCache {
+		return exist
+	}
+
+	if c.gitRepo == nil {
+		r, closer, err := gitrepo.RepositoryFromContextOrOpen(c.ctx, c.gitRepoFacade)
+		if err != nil {
+			log.Error("unable to open repository: %s Error: %v", gitrepo.RepoGitURL(c.gitRepoFacade), err)
+			return false
+		}
+		c.gitRepo, c.gitRepoCloser = r, closer
+	}
+
+	exist = c.gitRepo.IsReferenceExist(commitID) // Don't use IsObjectExist since it doesn't support short hashs with gogit edition.
+	c.commitCache[commitID] = exist
+	return exist
+}