fix: improve MCP server plugin path handling and backward compatibility for argsPosition #15970

Job	Run time
build (shenyu-integrated-test-grpc)	10m 16s
build (shenyu-integrated-test-motan)	10m 39s
build (shenyu-integrated-test-apache-dubbo)	9m 21s
build (shenyu-integrated-test-combination)	13m 32s
build (shenyu-integrated-test-http)	12m 44s
build (shenyu-integrated-test-sdk-http)	9m 28s
build (shenyu-integrated-test-sofa)	12m 8s
build (shenyu-integrated-test-sdk-apache-dubbo)	11m 23s
build (shenyu-integrated-test-https)	10m 47s
build (shenyu-integrated-test-websocket)	10m 19s
build (shenyu-integrated-test-spring-cloud)	12m 21s
build (shenyu-integrated-test-rewrite)	10m 18s
	2h 13m 16s

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