[Backport release-3_40] [ui] Fix missing @cluster_size and @cluster_color variables not visible when editing the cluster renderer's cluster symbol #36843

Job	Run time
build (24.04, 5, true, OFF, ON, ON, ON, ON, OFF, OFF, OFF, OFF, ON, false)	1h 48m 33s
build (39, 6, true, ON, OFF, ON, ON, OFF, OFF, ON, ON, ON, OFF, false)	3h 7m 23s
clang-tidy (24.04, 5)	5m 6s
Run tests (5, ALL_BUT_PROVIDERS)	29m 50s
Run tests (5, POSTGRES)	7m 47s
Run tests (5, HANA)	13m 16s
Run tests (6, ALL_BUT_PROVIDERS)	39m 22s
Run tests (5, ORACLE, 24.04, binary-for-oracle)	7m 49s
	6h 39m 6s

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