use enumerable: false for temporary no-longer-exists getters

[Conduitry]

There are a few objects in the codebase with getters that give more helpful errors messages that describe what features have replaced these removed/renamed features. However, these getters are also triggered when doing an object { ...spread }, which isn't very helpful. This updates these to use Object.definedProperties so that we may specify enumerable: false on these getters.

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[benmccann]

this is to provide a load wrapper with a fetch that provides a base URL? that sounds handy and like something I would use and I've seen other people ask for. what do you think about adding that to the FAQ?

[Rich-Harris]

@benmccann for fetch specifically, the intent was to let server-only load functions use the same fetch as shared load functions, so that specific case would no longer be necessary.

There are other times it would be useful to do this, but right now we're stymied by url being a getter:

kit/packages/kit/src/runtime/client/client.js

Lines 536 to 539 in b335f38

	get url() {
	uses.url = true;
	return load_url;
	},

In #6056 I plan to replace that with a TrackedURL object that only triggers the dependency tracking on accessing things like pathname and toString (not origin or hostname, because those can't change), instead of url itself.

(parent is too, but it actually doesn't need to be — we only need to care about invocation, not access.)

There's also event.clientAddress, which I think we'll need to change to event.getClientAddress() so that we can promote patterns that use object spread (and also use it ourselves).