more abstraction about ArrayLiteralExp.elements

[WalterBright]

towards fixing #23552

[github-actions]

DMD perf check

Metric	Base	PR	delta
compile hello.d (instr)	216.1 M	216.1 M	+0.02%
compile hello.d -O (instr)	234.6 M	234.6 M	+0.01%
compile Phobos (instr)	5,137.3 M	5,143.3 M	+0.12%
compile Phobos codegen (instr)	1,474.6 M	1,474.7 M	+0.01%
compile vibe.d (instr)	15,162.2 M	15,178.4 M	+0.11%
dmd binary size (stripped)	6.92 MB	6.94 MB	+0.23%
hello binary size	0.72 MB	0.72 MB	0.00%
peak RSS (compile hello.d)	44 MB	44 MB	-0.15%
peak RSS (compile Phobos)	638 MB	636 MB	-0.22%
peak RSS (compile vibe.d)	1979 MB	1979 MB	-0.03%