Proposal-temporal: `_repr_` should always return the same as `toString()`

[justingrant]

Repro:

Temporal.Instant.fromEpochMilliseconds(0).toString();
// => 1970-01-01T00:00:00Z
Temporal.Instant.fromEpochMilliseconds(0)._repr_
// => 1970-01-01T00:00:00+00:00

Not sure if this problem exists in other types, but should be checked.

[ljharb]

What is _repr_?

[ptomato]

It's not part of the proposal, it's a debugging aid that we add to the polyfill if you bundle it with a magic debug switch. The reason for it is so that a string representation shows up in browser devtools, instead of something like [Object Temporal.Instant] {}.