Buggy field visibility handling inobjectHas in Go impl

[mkmik]

The Go jsonnet implementation of std.objectHas and std.objectHasEx(...,..., false) doesn't correctly honour the field visibility if an object is extended. Instead, it only checks whether the field is visible in the "current" object, even if the field is hidden in super:

How to reproduce:

std.objectHasEx({"x":: null} + {"x": null}, "x", false)

Expected value: false

Actual value: true

The C++ implementation of std.objectHascorrectly returnsfalse`.

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Since std.get(.... inc_hidden=false) is implemented in terms of std.objectHas, that function is also buggy:

std.get(o={a:: 17} + {a: 18}, f="a", default=42, inc_hidden=false)

Expected value: 42

Actual value: 18

The C++ impl of std.get returns 42