chore: migrate java-firestore to google-cloud-java #17265

Job	Run time
owlbot-py	1m 17s
root-pom	1m 50s
gapic-bom	1m 45s
generate-readme	1m 13s
group_id_check_for_maps_libraries	8m 2s
owlbot-yaml	1m 10s
gitignore_correctness	1m 1s
package_name_check	59s
	17m 17s

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