fix: copy a Java array when spreading it

[marevol]

Stacked on #54.

Spreading a Java array of a reference type produced an array that shared storage with it, against the "a new array holding the elements" the method documents:

var StringArray = Java.type("java.lang.String[]");
var a = new StringArray(2); a[0] = "x"; a[1] = "y";
var js = [...a];

js[0] = "changed";   // a is now changed,y
js[0] = 42;          // java.lang.ArrayStoreException: java.lang.Integer
js[1] = {};          // java.lang.ArrayStoreException: ...JO4

Both come out of an ordinary assignment as raw Java exceptions, which script code cannot recover from.

Cause

toApplyArgs returns the very array it is given when that array is an Object[], and Global.allocate wraps rather than copies — ArrayData.allocate(Object[]) makes an ObjectArrayData over the same storage. Every other branch of TO_ARRAY builds a fresh array, and the start > 0 path already copied with Arrays.copyOfRange; only this one aliased.

Fix

Copy with Arrays.copyOf(array, length, Object[].class) rather than clone(), because a String[] clones to a String[]: the component type has to go too, or the second and third lines above still throw.

Verification

./gradlew build testOptimistic testPessimistic

suite	before	after
test	665, 0 fail	665, 0 fail
testOptimistic	1717, 0 fail	1717, 0 fail
testPessimistic	1717, 0 fail	1717, 0 fail