feat(core,isthmus): support grouping set index in Aggregate #1598

Job	Run time
Security validation	7s
Check editorconfig	4s
Lint commits for semantic-release	14s
osv-scanner (core)	1m 32s
osv-scanner (isthmus)	1m 42s
Build Examples	4m 5s
Build and Test Java	5m 4s
osv-scanner (isthmus-cli)	1m 51s
Dry-run release	24s
Build Isthmus Native Image (macOS-latest)	34m 30s
Build Isthmus Native Image (ubuntu-latest)	8m 31s
	58m 4s

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