Make repeated field merging consistent

[jcready]

This addresses https://github.com/timostamm/protobuf-ts/discussions/319

Setup

const source = { bars: [1],    foos: [{ foo: 1 }] };
const target = { bars: [2, 3], foos: [{ foo: 2 }, { foo: 3 }] };
reflectionMergePartial(SomeMessageType, target, source);

Before PR

Repeated Field	Scalar/Enum	Message
result target array is referentially equal to original target array	:x:	:white_check_mark:
result target array is deeply equal to source array	:white_check_mark:	:x:
result target array is NOT referentially equal to source array	:white_check_mark:	:white_check_mark:

After PR

Repeated Field	Scalar/Enum	Message
result target array is referentially equal to original target array	:white_check_mark:	:white_check_mark:
result target array is deeply equal to source array	:white_check_mark:	:white_check_mark:
result target array is NOT referentially equal to source array	:white_check_mark:	:white_check_mark: