avm2: Add CustomConstructor metadata to define custom native constructors #26462

Job	Run time
Paths filter	10s
Check dependencies	1m 27s
Lints with Rust stable	4m 33s
Test Rust stable / ubuntu-24.04	4m 47s
Lints with Rust beta	4m 32s
Test Rust stable / windows-latest	11m 7s
Lints with Rust nightly	4m 16s
Test Rust stable / macos-14	4m 58s
Test Rust ${{ matrix.rust_version }} / ${{ matrix.os }}	0s
Test Rust nightly / ubuntu-24.04	4m 34s
Test Rust beta / ubuntu-24.04	5m 49s
	46m 13s

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