Add `list_length` scalar function #4418

Job	Run time
Rust tests (tsan)	6m 28s
Rust/C++ FFI tests (tsan)	2m 8s
Rust/C++ FFI tests (asan)	2m 24s
Rust tests (miri)	1m 37s
Rust tests (asan)	6m 59s
Mirror DuckDB to R2 / Resolve DuckDB version and check R2	4s
DuckDB libraries available in R2	2s
Mirror DuckDB to R2 / Mirror DuckDB ${{ matrix.archive }} to R2	-1s
Rust tests (coverage) (tests)	6m 27s
	26m 8s

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