feat: generate a GAPIC library from api definition #8250

Job	Run time
build (11)	14m 51s
build (17)	15m 1s
build(21) except self-service clients	13m 28s
build(8) except for gapic-generator-java	4m 28s
build(8) for gapic-generator-java	11m 31s
compatibility	1m 34s
dependency_analyzer_unit_test	16s
gapic-generator-java-bom	1m 52s
showcase (11)	4m 34s
lint	23s
showcase (17)	4m 5s
showcase (21)	4m 10s
showcase-clirr	3m 7s
showcase-native	8m 10s
unmanaged_dependency_check	4m 9s
	1h 31m 39s

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