feat: use go:embed to embed templates (#1756)

tools/goctl/api/javagen/packet.tpl

@@ -0,0 +1,25 @@
+package com.xhb.logic.http.packet.{{.packet}};
+
+import com.xhb.core.packet.HttpPacket;
+import com.xhb.core.network.HttpRequestClient;
+{{.imports}}
+
+{{.doc}}
+public class {{.packetName}} extends HttpPacket<{{.responseType}}> {
+	{{.paramsDeclaration}}
+
+	public {{.packetName}}({{.params}}{{if .HasRequestBody}}{{.requestType}} request{{end}}) {
+		{{if .HasRequestBody}}super(request);{{else}}super(EmptyRequest.instance);{{end}}
+		{{if .HasRequestBody}}this.request = request;{{end}}{{.paramsSetter}}
+    }
+
+	@Override
+    public HttpRequestClient.Method requestMethod() {
+        return HttpRequestClient.Method.{{.method}};
+    }
+
+	@Override
+    public String requestUri() {
+        return {{.uri}};
+    }
+}