[JAVA] [PERF] improve java enum fromValue generation #1098

Job	Run time
Build Java Client JDK8 (samples/client/echo_api/java/feign-gson)	1m 5s
Build Java Client JDK8 (samples/client/echo_api/java/okhttp-gson)	1m 24s
Build Java Client JDK8 (samples/client/echo_api/java/resttemplate)	1m 23s
Build Java Client JDK8 (samples/client/echo_api/java/apache-httpclient)	1m 36s
Build Java Client JDK8 (samples/client/echo_api/java/resteasy)	1m 16s
	6m 44s

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