https://tc39.es/ecma262/#sec-properties-of-the-array-prototype-object
The Array prototype object: [...] is an Array exotic object and has the
internal methods specified for such objects.
NOTE: The Array prototype object is specified to be an Array exotic
object to ensure compatibility with ECMAScript code that was created
prior to the ECMAScript 2015 specification.
This was not implementing the following part of the spec correctly:
27. For each integer i such that i ≥ 1 and i ≤ n, do
a. Let captureI be ith element of r's captures List.
b. If captureI is undefined, let capturedValue be undefined.
Expecting a capture group match to exist for each of the RegExp's
capture groups would assert in Vector's operator[] if that's not the
case, for example:
/(foo)(bar)?/.exec("foo")
Append undefined instead.
Fixes#5256.
If we have a function as class extends value, we still cannot assume
that it has a prototype property and that property has a function or
null as its value - blindly calling to_object() on it may fail.
Fixes#5075.
