Fix markdown preview $$ support (#31514)

close #31481

currently `$$A + B$$ test` will ignore text after $$ block

test text

![圖片](https://github.com/go-gitea/gitea/assets/30816317/39b2974b-c0b6-48a0-87d0-5f4a13615eed)

before fix

![圖片](https://github.com/go-gitea/gitea/assets/30816317/15469e4c-474d-4128-b46f-d6cadaafbd68)

after fix

![圖片](https://github.com/go-gitea/gitea/assets/30816317/c1025eef-177f-4ade-988f-510e7039f3f9)

github display

![圖片](https://github.com/go-gitea/gitea/assets/30816317/97cd1e10-ac94-4899-86d8-8e359ef1d694)

modules/markup/markdown/math/inline_renderer.go

@@ -21,7 +21,11 @@ func NewInlineRenderer() renderer.NodeRenderer {
 
 func (r *InlineRenderer) renderInline(w util.BufWriter, source []byte, n ast.Node, entering bool) (ast.WalkStatus, error) {
 	if entering {
-		_, _ = w.WriteString(`<code class="language-math is-loading">`)
+		extraClass := ""
+		if _, ok := n.(*InlineBlock); ok {
+			extraClass = "display "
+		}
+		_, _ = w.WriteString(`<code class="language-math ` + extraClass + `is-loading">`)
 		for c := n.FirstChild(); c != nil; c = c.NextSibling() {
 			segment := c.(*ast.Text).Segment
 			value := util.EscapeHTML(segment.Value(source))
@@ -43,4 +47,5 @@ func (r *InlineRenderer) renderInline(w util.BufWriter, source []byte, n ast.Nod
 // RegisterFuncs registers the renderer for inline math nodes
 func (r *InlineRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
 	reg.Register(KindInline, r.renderInline)
+	reg.Register(KindInlineBlock, r.renderInline)
 }