chore: migrate java-firestore to google-cloud-java #17354

Job	Run time
gapic-bom	1m 39s
generate-readme	1m 5s
root-pom	1m 49s
package_name_check	1m 1s
owlbot-yaml	1m 0s
group_id_check_for_maps_libraries	8m 6s
gitignore_correctness	1m 1s
owlbot-py	1m 11s
	16m 52s

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