Should Safari 15.4 have its own entry?

[JohnRiv]

I noticed both .at() method on the built-in indexables and Object.hasOwn were added to Safari in v15.4. It's unclear looking at the current table that the currently supported Safari version supports those.

I tested it to confirm the support is there, and it is also confirmed by:

• Apple's release notes
• MDN:
  • Array.prototype.at()
  • String.prototype.at()
  • TypedArray.prototype.at()
  • Object.hasOwn()

[ljharb]

Yes, whenever a new feature is added to an env, we add a new entry to differentiate.

As such, https://github.com/kangax/compat-table/blob/9742598c5883018d68885e766840b4c5d7efab8f/environments.json#L3264-L3277 should be extended to include safari15_3, and safari15_4, so that "safari15" points to the latest, and we can then identify for these features "the last version that didn't have it" and "the first version that did".