Fix the problem of showing 500 error while containing special chars in excerpt (#5263)

#### What type of PR is this?

/kind bug
/area core
/milestone 2.12.0

#### What this PR does / why we need it:

This PR refactors building html meta by using `modelFactory#createStandaloneElementTag`.

See https://github.com/halo-dev/halo/issues/4755 for more.

#### Which issue(s) this PR fixes:

Fixes https://github.com/halo-dev/halo/issues/4755

#### Special notes for your reviewer:

Validate via <https://github.com/halo-dev/halo/issues/4755#issuecomment-1776391345>.

#### Does this PR introduce a user-facing change?

```release-note
修复摘要中包含特殊字符导致无法解析页面的问题
```

application/src/main/java/run/halo/app/theme/dialect/ContentTemplateHeadProcessor.java

@@ -2,11 +2,13 @@ package run.halo.app.theme.dialect;
 
 import static org.apache.commons.lang3.ObjectUtils.defaultIfNull;
 import static org.apache.commons.lang3.StringUtils.defaultIfBlank;
+import static org.thymeleaf.model.AttributeValueQuotes.DOUBLE;
 
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.stream.Collectors;
 import lombok.AllArgsConstructor;
 import org.apache.commons.lang3.StringUtils;
 import org.springframework.core.annotation.Order;
@@ -15,6 +17,7 @@ import org.springframework.web.util.HtmlUtils;
 import org.thymeleaf.context.ITemplateContext;
 import org.thymeleaf.model.IModel;
 import org.thymeleaf.model.IModelFactory;
+import org.thymeleaf.model.ITemplateEvent;
 import org.thymeleaf.processor.element.IElementModelStructureHandler;
 import reactor.core.publisher.Mono;
 import run.halo.app.theme.DefaultTemplateEnum;
@@ -62,11 +65,9 @@ public class ContentTemplateHeadProcessor implements TemplateHeadProcessor {
         }
 
         return htmlMetasMono
-            .doOnNext(htmlMetas -> {
-                String metaHtml = headMetaBuilder(htmlMetas);
-                IModelFactory modelFactory = context.getModelFactory();
-                model.add(modelFactory.createText(metaHtml));
-            })
+            .doOnNext(
+                htmlMetas -> buildMetas(context.getModelFactory(), htmlMetas).forEach(model::add)
+            )
             .then();
     }
 
@@ -97,19 +98,12 @@ public class ContentTemplateHeadProcessor implements TemplateHeadProcessor {
         String CONTENT = "content";
     }
 
-    private String headMetaBuilder(List<Map<String, String>> htmlMetas) {
-        if (htmlMetas == null) {
-            return StringUtils.EMPTY;
-        }
-        StringBuilder sb = new StringBuilder();
-        for (Map<String, String> htmlMeta : htmlMetas) {
-            sb.append("<meta");
-            htmlMeta.forEach((k, v) -> {
-                sb.append(" ").append(k).append("=\"").append(v).append("\"");
-            });
-            sb.append(" />\n");
-        }
-        return sb.toString();
+    private List<ITemplateEvent> buildMetas(IModelFactory modelFactory,
+        List<Map<String, String>> metas) {
+        return metas.stream()
+            .map(metaMap ->
+                modelFactory.createStandaloneElementTag("meta", metaMap, DOUBLE, false, true)
+            ).collect(Collectors.toList());
     }
 
     private boolean isPostTemplate(ITemplateContext context) {

application/src/main/java/run/halo/app/theme/dialect/DuplicateMetaTagProcessor.java

@@ -12,6 +12,7 @@ import org.springframework.core.annotation.Order;
 import org.springframework.stereotype.Component;
 import org.thymeleaf.context.ITemplateContext;
 import org.thymeleaf.model.IModel;
+import org.thymeleaf.model.IProcessableElementTag;
 import org.thymeleaf.model.ITemplateEvent;
 import org.thymeleaf.model.IText;
 import org.thymeleaf.processor.element.IElementModelStructureHandler;
@@ -59,9 +60,19 @@ public class DuplicateMetaTagProcessor implements TemplateHeadProcessor {
                 IText otherText = context.getModelFactory()
                     .createText(text);
                 otherModel.add(new IndexedModel(i, otherText));
-            } else {
-                otherModel.add(new IndexedModel(i, templateEvent));
+                continue;
             }
+            if (templateEvent instanceof IProcessableElementTag tag) {
+                var indexedModel = new IndexedModel(i, tag);
+                if ("meta".equals(tag.getElementCompleteName())) {
+                    var attribute = tag.getAttribute("name");
+                    if (attribute != null) {
+                        uniqueMetaTags.put(attribute.getValue(), indexedModel);
+                        continue;
+                    }
+                }
+            }
+            otherModel.add(new IndexedModel(i, templateEvent));
         }
 
         otherModel.addAll(uniqueMetaTags.values());

application/src/test/java/run/halo/app/theme/dialect/ContentTemplateHeadProcessorIntegrationTest.java

@@ -146,8 +146,8 @@ class ContentTemplateHeadProcessorIntegrationTest {
              <head>
               <meta charset="UTF-8">
               <title>Post detail</title>
-              <meta name="description" content="post-description">
               <meta name="keyword" content="postK1,postK2">
+              <meta name="description" content="post-description">
               <meta name="other" content="post-other-meta">
              </head>
              <body>

application/src/test/java/run/halo/app/theme/dialect/HaloProcessorDialectTest.java

@@ -174,9 +174,9 @@ class HaloProcessorDialectTest {
                 <title>Post</title>
               <meta name="global-head-test" content="test" />
             <meta name="content-head-test" content="test" />
-            <meta content="post-meta-V1" name="post-meta-V1" />
-            <meta content="post-meta-V2" name="post-meta-V2" />
-            <meta name="description" content="" />
+            <meta content="post-meta-V1" name="post-meta-V1"/>\
+            <meta content="post-meta-V2" name="post-meta-V2"/>\
+            <meta name="description" content=""/>\
             </head>
               <body>
                 <p>post</p>