chore: improve monorepo migration tooling #20273

Job	Run time
windows	2m 27s
lint	4m 23s
bulk-filter	57s
enforcer	18m 31s
changes	3s
generation-config-check	1m 35s
gapic-libraries-bom	18m 24s
split-units (java-datastore, 8)	3m 1s
split-units (java-datastore, 17)	4m 35s
split-dependencies (java-datastore)	4m 8s
split-units (java-datastore, 11)	3m 24s
split-clirr (java-datastore)	2m 18s
split-units (java-datastore, 25)	4m 36s
split-units (java-datastore, 21)	4m 43s
units (8)	33m 38s
units (11)	33m 39s
units (17)	33m 42s
units (25)	34m 7s
units (21)	31m 47s
conditional-required-check	2s
	4h 0m 0s

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