Remove [this-escape] warnings in generated ApiClient classes (#21620) #203

Job	Run time
Build Java Server (samples/server/petstore/java-inflector/)	56s
Build Java Server (samples/server/petstore/java-microprofile/)	59s
Build Java Server (samples/server/petstore/java-vertx-web/)	47s
Build Java Server (samples/server/petstore/java-pkmst/)	55s
	3m 37s

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