Refactor markup render system (#32589)

This PR mainly moves some code and introduces `RenderContext.WithXxx`
functions

modules/markup/csv/csv_test.go

@@ -4,10 +4,10 @@
 package markup
 
 import (
+	"context"
 	"strings"
 	"testing"
 
-	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/markup"
 
 	"github.com/stretchr/testify/assert"
@@ -24,8 +24,7 @@ func TestRenderCSV(t *testing.T) {
 
 	for k, v := range kases {
 		var buf strings.Builder
-		err := render.Render(&markup.RenderContext{Ctx: git.DefaultContext},
-			strings.NewReader(k), &buf)
+		err := render.Render(markup.NewRenderContext(context.Background()), strings.NewReader(k), &buf)
 		assert.NoError(t, err)
 		assert.EqualValues(t, v, buf.String())
 	}